Obama: 'Do not foresee scenario' of American boots on ground in Syria

(CNN) -- U.S. President Barack Obama does not foresee a scenario of "American boots on the ground in Syria," telling reporters Friday that it would not be good for the United States or for that county.

"As a general rule, I don't rule things out as commander-in-chief, because circumstances change," Obama said during a joint news conference with President Laura Chinchilla of Costa Rica, where the president stopped during a three-day visit to the region.

"Having said that, I do not foresee a scenario in which boots on the ground in Syria, American boots on the ground in Syria, would be good for America or be good for Syria."

Obama said he has consulted with leaders in the region who want to see stability return to Syria, and "they agree with that assessment."

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Even so, the president said that if the United States confirms the use of chemical weapons by the Syrian government against its people, "that's a game changer for us."

He did not elaborate on what steps would be taken, repeating as he has said previously that the United States would wait until it has more details of evidence of chemical weapons use in Syria before making any decision on whether to alter strategy.

"We have evidence that chemical weapons have been used. We don't know when, where or how they were used," Obama said.

Obama's assessment was supported by Michael Oren, Israel's ambassador to the United States.

"This was a military assessment of intelligence; like all intelligence assessments, there's no absolute certitude," he told CNN's Jake Tapper on Friday. "Our assessment was confirmed by British, French and American sources. But it's true that the usage of chemical weapons by the Syrian regime or anybody in Syria is being closely monitored by our intelligence agency and continues to be discussed at the highest levels between the Israeli and U.S. governments."

But in recent days, the Pentagon has stepped up planning for potential military intervention in Syria, which would most likely include the use of fighter jets and cruise missiles, two administration officials who were not authorized to publicly discuss the matter told CNN.

For now, Obama said, the United States is continuing its investigation, and working with its Middle East and European allies.

The president's comments follow a number of claims in recent weeks that the Syrian government has used chemical weapons against its people in a more than two-year civil war. The United Nations estimates some 70,000 people have died in the fighting.

Syria had denied the use of chemical weapons, accusing the United States of manipulating evidence to pressure President Bashar al-Assad to step down.

Obama has been under fire by some in the United States, including Sen. John McCain, R-Arizona, for not taking a tougher stance with Syria.

The president said the United States is "not waiting."

"We are not standing by," he said, adding that the United States has been the largest contributor of humanitarian aid and nonlethal aid to the opposition.

"We are actively engaged on a day-to-day basis to deal with this crisis to restore a Syria that is respectful of the rights and aspirations of the Syrian people."

In addition to Syria's possible use of chemical weapons against rebels, another concern is that parts of the government's stockpile of chemical weapons -- which analysts believe is one of the world's largest and includes sarin, mustard and VX gases -- could end up, if they haven't already, in others' hands.

CNN's Barbara Starr contributed to this report.