(CNN) -- Syria's president made a rare public appearance Wednesday.
Bashar al-Assad visited the Umawyeen Electricity Station at Tishreen Park in Damascus to commemorate Workers' Day. He congratulated the station's staff and all other Syrian workers.
The visit came amid more violence in the civil war, a 2-year-old conflict fueled by a grass-roots revolt against the government. At least 50 people were killed Wednesday, the opposition Local Coordination Committees of Syria said.
The opposition Syrian Observatory for Human Rights said regime aircraft bombarded targets in the Damascus countryside and Aleppo province.
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The group said an improvised explosive device detonated near a police headquarters in Damascus, injuring a number of people, including children.
A giant plume of thick, gray smoke rose over central Damascus, hanging over the skyline. It was not immediately known if there were any fatalities.
According to the state-run Syrian Arab News Agency, four people, including a 10-year-old child, were killed, and more than two dozen wounded in a series of bomb blasts in Damascus
Two of the explosive devices were planted on bicycles, SANA said, blaming the violence on terrorists.
Hezbollah and Syria
Hezbollah has threatened to intervene further in Syria if there is any threat that the regime could fall to the United States, Israel or extremists, the Lebanese militant group said.
The radical Shiite group, which the United States and Israel call a terrorist organization, has said it is in Syria only to protect Lebanese in the country and to protect holy Shiite shrines from the warfare.
But reports emerged months ago that Hezbollah fighters are battling Syrian rebels near the Lebanese border.
On Tuesday, Hezbollah leader Hassan Nasrallah said the group could step up its presence in Syria and issued an ominous warning to opposition members backed by foreigners who may try to overthrow al-Assad's regime.
"Syria has real friends in the region and the world. And they will never allow Syria to fall to the hands of the United States, Israel or extremist groups. They will never allow it. You may ask how will this happen. The details will come later," Nasrallah said.
Sectarian strife has been a factor in the civil strife.
The majority of the country is Sunni Muslim; al-Assad's family is Alawite, an offshoot of Shiite Islam.
The Hezbollah leader expressed concern that some Sunni extremists may try to destroy holy Shiite shrines in Syria. While such shrines are highly revered by Shiites, a number of Sunni radicals believe they amount to sacrilege.
One of the most notable shrines is the Sayida Zeinab, which Shiites believe houses the tomb of the Prophet Mohammed's granddaughter, Zeinab. It's located about 10 kilometers (6 miles) south of the Syrian capital.
"Some extremist groups plan to execute their threats with regards to (Sayida Zeinab), and if such a crime were to take place, it will carry with it grave consequences," Nasrallah said.
But the Syrian National Coalition, an umbrella opposition group, dismissed the Hezbollah leader's claims.
"Only the Syrians are responsible to defend and protect their cities and their holy shrines. We don't need the regime militias or Hezbollah fighters to tell us what our duty is," the council said in a statement. "This is our land, our country and our future."
Russia says ships ready to evacuate citizens
The commander of a group of Russian warships said his forces are prepared to evacuate Russian citizens from Syria.
Captain Alexei Komarov said ships due to participate in military exercises off the Syrian coast are standing ready, according to the state-run news agency Itar-Tass.
At least one ship, the Azov, is ported in the Israeli coastal city of Haifa.
There are between 35,000 and 40,000 Russian families in Syria, the Syrian Ambassador to Russia, Riyad Haddad, said last week. He added that only about 100 families have returned to Russia since the start of the civil war. They were relocated in January after being bused out of the country.
A large-scale evacuation from the Syrian coast would be a shift in confidence for Moscow, which has been a staunch ally of Damascus and the al-Assad government.
The Russian military maintains a small base and uses the Syrian port of Tartus for resupply missions.
READ MORE: World seeks answers as Syria civil war evolves
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CNN's Holly Yan contributed to this report.
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Multiple explosions hit a Syrian village near the Israeli border on May 6.
A photo released by the Syrian Arab News Agency shows destruction from what is said was bomb attack in the Al-Hama area of Damascus on Sunday, May 5. According to the Syrian government, Israel launched an attack on a research center in the Damascus suburbs early Sunday.
People run for cover after what activists said was shelling by forces loyal to Syria's President Bashar al-Assad in Syria's Raqqa province, on May 3.
People walk past a damaged building and multiple destroyed cars at the site of an explosion in Damascus where at least 13 were killed on April 30.
Cleaning takes place following another explosion in an upscale Damascus neightborhood on Monday, April 29. Syrian Prime Minister Wael al-Halqi survived the bombing targeting his motorcade.
A smoke cloud rises from shelling on the the al-Turkman mountains in Syria's Latakia province on Thursday, April 25.
Searchers use a flashlight as they look for survivors among the rubble created by what activists say was a missile attack from the Syrian regime, in Raqqa province, Syria, on April 25.
A handout photograph from Syria's national news agency SANA shows damage and debris from a mortar attack in the suburb of Jarmana near Damascus, Syria, on Wednesday, April 24. The attack killed seven and wounded more than 25, according to activists and state media. No group claimed responsibility for the mortar fire, which SANA said hit a municipality office and a school building.
A Kurdish fighter from the "Popular Protection Units" (YPG) takes position inside a building in the majority-Kurdish Sheikh Maqsood area of Aleppo, on Apri. 21.
People walk past destroyed houses in the northern Syrian town of Azaz on Sunday, April 21.
Free Syrian Army fighters take positions prior to an offensive against government forces in the Khan al-Assal area, near Aleppo on Saturday, April 20.
Men inspect damage at a house destroyed in an airstrike in Aleppo on April 15.
Syrian and Kurdish rebel fighters walk in the Sheikh Maqsud district of Aleppo on April 14.
A Syrian boy holds an AK-47 assault rifle in the streets of Aleppo on Sunday, April 14.
A female rebel monitors the movement of Syrian government forces in Aleppo's Sheikh Maqsud neighborhood on April 11.
A rebel runs to avoid sniper fire from Syrian government forces in Aleppo on Thursday, April 11.
Syrian rebels observe the movement of Syrian government forces around Al-Kendi hospital in Aleppo on Wednesday, April 10.
Rescue teams and security forces check out the scene of a deadly car bomb explosion in Damascus on April 8.
The fighting has taken a toll on buildings in Aleppo's Saladin district, seen here on April 8.
A Syrian rebel runs for cover in Deir ez-Zor on April 2.
A rebel checks for snipers across the street toward the Citadel in Aleppo, Syria, on Saturday, March 30, in this photo taken by iReporter Lee Harper.
A Free Syrian fighter mourns the death of a friend in Aleppo on March 30, in this photo taken by iReporter Lee Harper.
A Syrian opposition fighter runs for cover from Syrian army snipers in Aleppo on Wednesday, March 27.
A Syrian girl covers her face to protect herself from fumes as a street covered with uncollected garbage is fumigated in Aleppo on Sunday, March 24.
A Syrian man and his family drive past damaged buildings in Maarat al-Numan, on Wednesday, March 20.
Syrians carry the body of a Syrian army soldier during a funeral ceremony in Idlib province on Tuesday, March 19.
Syrian rebels take position in Aleppo, the largest city in the country, on March 11.
Syrian men search for their relatives amongst the bodies of civilians executed and dumped in the Quweiq River on March 11.
A Free Syrian Army fighter looks back as smoke rises during fighting between rebel fighters and forces loyal to Syria's President Bashar al-Assad on the outskirts of Aleppo on Saturday, March 2.
Residents read Shaam News newspapers published by the Free Syrian Army in Aleppo on March 2.
A member of the Free Syrian Army reacts to the death of a comrade who was killed in fighting, at Bustan al Qasr cemetery in Aleppo on Friday, March 1.
A rebel fighter throws a home-made grenade at Syrian government forces in Aleppo on February 16.
A member of the Free Syrian Army stands with his weapon as he looks at a rainbow in Aleppo on February 16.
A Syrian woman looks through a bus window in Aleppo on February 14.
Free Syrian Army fighters walk through a dust-filled stairwell in Damascus on February 7.
A Syrian rebel gestures at comrades from inside a broken armored personnel carrier in Al-Yaqubia on February 6.
A rebel fighter throws a hand grenade inside a Syrian Army base in Damascus on February 3.
People stand in the dust of a building destroyed in an airstrike in Aleppo, Syria on February 3.
Free Syrian Army fighters run as they enter a Syrian Army base during heavy fighting in the Arabeen neighborhood of Damascus on February 3.
An unexploded mortar shell fired by the Syrian Army sits lodged in the ground in Damascus on January 25.
Fighters from Fateh al Sham unit of the Free Syrian Army fire on Syrian Army soldiers at a check point in Damascus on January 20.
A Free Syrian Army fighter walks between buildings damaged during Syrian Air Force strikes in Damascus on January 19.
A Syrian rebel fighter tries to locate a government jet fighter in Aleppo on January 18.
Syrian rebels launch a missile near the Abu Baker brigade in Albab on January 16.
A Syrian boy walks near rubbish next to tents at a refugee camp near the northern city of Azaz on the Syria-Turkey border, on January 8.
Syrians look for survivors amid the rubble of a building targeted by a missile in Aleppo on January 7.
A father reacts after hearing of a shelling by forces loyal to Syria's President Bashar al-Assad in Aleppo on January 3.
A patient smokes a cigarette at Dar Al-Ajaza psychiatric hospital in Aleppo on December 18, 2012. The psychiatric ward, housing around 60 patients, has lacked the means to function properly since fighting broke out there in July.
Syrians mourn a fallen rebel fighter at a rebel base in the al-Fardos area of Aleppo on December 8.
Members of Liwa (Brigade) Salahadin, a Kurdish military unit fighting alongside rebel fighters, monitor the area in the besieged district of Karmel al-Jabl in Aleppo on December 6.
A member of Liwa Salahadin aims at a regime fighter in the besieged district of Karmel al-Jabl in Aleppo on December 6.
Two young boys sit underneath a washline in a refugee camp on the border between Syria and Turkey near Azaz on December 5.
The bodies of three children, who were allegedly killed in a mortar shell attack that landed close to a bakery in Aleppo, on December 2, are laid out for identification by family members at a makeshift hospital at an undisclosed location of the city.
Smoke rises in the Hanano and Bustan al-Basha districts in Aleppo on December 1 as fighting continues through the night.
Damaged houses in Aleppo are seen after an airstrike on November 29.
A Syrian rebel mourns the death of a comrade in Maraat al-Numan on November 20.
Syrians protesters stand on Assad's portrait during an anti-regime demonstration in Aleppo on November 16.
A Syrian rebel takes cover during fighting against Syrian government forces in Aleppo on November 15.
Syrian opposition fighter Bazel Araj, 19, sleeps next to his pistol in Aleppo on November 11.
A rebel fighter fires at a Syrian government position in Aleppo on November 6.
A Syrian rebel leaps over debris left in the street while running across a "sniper alley" near the Salahudeen district in Aleppo on November 4.
Rebels hold their position in the midst of a battle on November 3 in Aleppo.
A man cries while being treated in a local hospital in a rebel-controlled area of Aleppo on October 31.
A man is treated for wounds after a government jet attacked the Karm al-Aser neighborhood in eastern Aleppo on October 31.
A Syrian rebel interrogates a handcuffed and blindfolded man suspected of being a pro-regime militiaman in Aleppo on October 26.
Smoke rises from a fuel station following a mortar attack as Syrian women walk on a rainy day in the Arqub neighborhood of Aleppo on October 25.
A Syrian rebel fires at an army position in the Karm al-Jabal district of Aleppo on October 22.
A wounded Syrian boy sits on the back of a truck carrying victims and wounded people to a hospital following an attack by regime forces in Aleppo on October 21.
A man lies on the ground after being shot by a sniper for a second time as he waits to be rescued by members of the Al-Baraa Bin Malek Battalion, part of the Free Syria Army's Al-Fatah brigade, in Aleppo on October 20.
Syrian army soldiers run for cover during clashes with rebel fighters at Karam al-Jabal neighborhood of Aleppo on October 20.
Smoke rises after a Syrian Air Force fighter jet fired missiles at the suburbs of the northern province of Idlib on October 16.
A Syrian opposition fighter stands near a post in Aleppo on October 11.
A Syrian man mourns the death of his father, who was killed during a government attack in Aleppo on October 10.
A rebel fighter is carried by his friends and laid on a gurney to be treated for gunshot wounds sustained during heavy battles with government forces in Aleppo on October 1.
Syrian rebels help a wounded comrade to an Aleppo hospital after he was injured in a Syrian army strike on September 18.
Free Syria Army fighters are reflected in a mirror they use to see a Syrian Army post only 50 meters away in Aleppo on September 16.
A Syrian man carrying grocery bags tries to dodge sniper fire as he runs through an alley near a checkpoint manned by the Free Syria Army in Aleppo on September 14.
A woman walks past a destroyed building in Aleppo on September 13.
Free Syrian Army fighters battle during street fighting against Syrian army soldiers in Aleppo on September 8.
A Syrian man wounded by shelling sits on a chair outside a closed shop in Aleppo on September 4.
A woman sits in her wheelchair next to her house, damaged by a Syrian air raid, near Homs on August 26.
Members of the Free Syrian Army clash with Syrian army soliders in Aleppo's Saif al-Dawla district on August 22.
A man mourns in front of a field hospital on August 21 in Aleppo.
Wounded civilians wait in a field hospital after an air strike on August 21 in Aleppo.
People pray during the funeral of a Free Syrian Army fighter, Amar Ali Amero, on August 21.
A man cries near the graves of his two children killed during a recent Syrian airstrike in Azaz on August 20.
A Syrian woman holds her dead baby as she screams upon seeing her husband's body being covered following an airstrike by regime forces on the town of Azaz on August 15.
A Syrian rebel runs in a street of Selehattin during an attack on the municipal building on July 23.
Syrian rebels hunt for snipers after attacking the municipality building in the city center of Selehattin on July 23.
Members of the Free Syrian Army's Mugaweer (commandos) Brigade pay their respects in a cemetery on May 12 in Qusayr.
Syrian rebels take position near Qusayr on May 10.
A Free Syrian Army member takes cover in underground caves in Sarmin on April 9.
Rebels prepare to engage government tanks that advanced into Saraquib on April 9.
Men say prayers during a ceremony in Binnish on April 9.
A young boy plays with a toy gun in Binnish on April 9.
A Free Syrian Army rebel mounts his horse in the Al-Shatouria village near the Turkish border in northwestern Syria on March 16, a year after the uprising began.
Syrian refugees walk across a field before crossing into Turkey on March 14.
A rebel takes position in Al-Qsair on January 27.
A protester in Homs throws a tear gas bomb back towards security forces, on December 27, 2011.
A man stands under a giant Syrian flag outside the Umayyad Mosque in Damascus on December 24, 2011.
A member of the Free Syrian Army looks out over a valley in the village of Ain al-Baida on December 15, 2011.
Members of the Free Syrian Army stand in an valley near the village of Ain al-Baida, close to the Turkish border, on December 15, 2011.
Displaced Syrian refugees walk through an orchard adjacent to Syria's northern border with Turkey on June 14, 2011, near Khirbet al-Jouz.
A Syrian man holds up a portrait of President Bashar al-Assad during a rally to show support for the president in Damascus on April 30, 2011.
Syrians rally to show their support for President Bashar al-Assad in Damascus on April 30, 2011.
A screen grab from YouTube shows thick smoke rising above as Syrian anti-government protesters demonstrate in Moaret Al-Noman on April 29, 2011.
A screen grab from YouTube shows Syrian anti-government protesters run for cover from tear gas fired by security forces in Damascus on April 29, 2011, during the "Day of Rage" demonstrations called by activists to put pressure on al-Assad.
Syrians wave their national flag and hold portraits of al-Assad during a rally to show their support for their leader in Damascus on March 29, 2011.
A woman sits by the hospital bed of a man allegedly injured when an armed group seized rooftops in Latakia on March 27, 2011, and opened fire at passers-by, citizens and security forces personnel according to official sources.
Syrian protesters chant slogans in support of al-Assad during a rally in Damascus on March 25, 2011.
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