3 dead in blast on Afghan prison wall

Kabul, Afghanistan (CNN) -- A blast on a prison wall in northern Afghanistan killed three inmates, a police official said Friday.

The incident took place Thursday in Sar-e-Pul, the capital of the northern province of the same name.

Lal Mohammad Ahmadzai, a police spokesman, said 20 prisoners were injured. Five tried to escape but were arrested.

SITE Intelligence Group, which tracks online militant activity, said the Afghan Taliban claimed that it freed 170 fighters and killed 13 "enemy troops."

A Taliban spokesman said in a website communique that fighters attacked guards and blew a hole into the main prison wall, SITE said.

"This successful operation demonstrates that the enemy deeply lacks the moral and military skills despite being deeply entrenched and still failing in protecting the prison," Taliban spokesman Muhammad Yusuf said.

Ahmadzai rejected the Taliban claims.

CNN's Masoud Popalzai contributed to this report.