In a statement on Sunday, Mujahid described the attack as “suspicious” and called on all Taliban members to maintain their positions across the country, according to Tasnim dispatches.
The Afghan Taliban called last week for its fighters to observe a three-day truce to coincide with a 10-day ceasefire declared by the Afghan government for Eid al-Fitr, the holiday marking the end of the Muslim holy month of Ramadan.
However, the ceasefire was violated after a bomber on Sunday targeted a gathering of Taliban members who were celebrating a three-day truce coinciding with the Eid al-Fitr holiday.
Mujahid stressed that no Taliban member is allowed to retreat from his position.
No one immediately claimed the attack, but it was likely carried out by Daesh (also known as ISIL or ISIS), which was not included in the ceasefire and has clashed with the Taliban in the past.
Later the terror group said in its Amaq website the attack on Saturday targeted "a gathering of Afghan forces" in Nangarhar, but gave no details.
After the attack, Afghan President Ashraf Ghani announced a nine-day extension of the cease-fire.