The blast targeted Afghan security forces in Pul-e-Alan, the capital of the Logar Province, Shahpoor Ahmadzai, spokesman for the provincial police, was cited by Reuters as saying.
Civilian casualties are also feared, he added.
Hasib Stanekkzai, head of the provincial council, announced the death toll to the agency, adding that 22 more people had also been wounded in the incident.
The Taliban, though, have denied any responsibility for the explosion.
The militants have announced the ceasefire on the occasion of the Muslim festivity of Eid al-Adha (Feast of Sacrifice) that marks the end of the annual Hajj pilgrimage.
Logar neighbors the country’s Nangarhar Province that has come to host the largest number of terrorists belonging to the Takfiri Daesh group over the recent years. The terrorists have staged some high-profile attacks across Afghanistan since suffering defeat in Syria and Iraq in late 2017.
The three-day ceasefire will begin on Friday. It has raised hopes of a permanent truce ahead of much-awaited peace talks between the Taliban and Kabul.