The chief of police for Zabul province in southeastern Afghanistan, Ghulam Saki Roghlewanai, said some explosives had been placed earlier near a prison wall. He said the explosion was triggered by a child although it wasn't clear whether the child did it intentionally.
After the explosion two Taliban prisoners inside tried to grab the weapons of the police guards, he said. The police managed to shoot and kill the two Taliban prisoners but two officers were also wounded in the incident, Roghlewanai said.
"It was a foiled prison break from the Taliban side. They were trying to get hold of prisoners from inside," he said.
The militants have staged some elaborate prison breaks to free their comrades, including a 2011 incident in Kandahar that freed more than 400 inmates. During that incident militants dug a 1,050-foot tunnel from a nearby house to the prison.