Militants attacked a major prison in eastern Afghanistan on Sunday, detonating a car bomb and waging a gun battle against guards for hours, as dozens of inmates managed to escape, Afghan officials said.

The attack, which continued into late Monday morning in the city of Jalalabad, came as the issue of releasing insurgent fighters from prison has moved to the forefront of efforts to strike a peace deal and end Afghanistan’s long war.

Disagreement over the last batch of a prisoner release has delayed the next steps of an agreement reached in February between the United States and the Taliban, and the start of direct talks between the Taliban and the Afghan government.

Zabihullah Mujahid, a spokesman for the Taliban, said the group was not behind the assault on the prison, which holds about 1,500 inmates

But other militant groups that are also fighting the government were not party to that agreement, and one of those, the Islamic State, claimed responsibility for the attack on Sunday through its Amaq news agency.