Armed men stormed a prison in eastern Afghanistan on Sunday killing at least one person and shattering the relative calm of a ceasefire across the country, an official said.

The gunmen set off an explosives-packed car near the prison before open firing on security guards at the facility in the city of Jalalabad, Attaullah Khogyani, the spokesman for the governor of Nangarhar province, told AFP.

"A number of them have taken position in a market near the prison and are engaging the security forces," he said.

"Fighting is continuing. So far one person has been killed and 18 more wounded."

The Taliban denied they were involved in the assault, that came on the final day of a rare truce between the insurgent group and Kabul to mark the Eid al-Adha holiday.

"This is not our attack. Our mujahideen are not yet authorised to carry out attacks," Taliban spokesman Zabihullah Mujahid told AFP.