Police said the blast took place inside a mosque in Shakardara district north of Kabul on Friday, as worshipers had gathered for Friday prayers on the second day of Eid al-Fitr holidays.
“The death toll has jumped to 12 killed, including the imam of the mosque, and 15 others are wounded,” said Ferdaws Framurz, a spokesman for Kabul police.
Earlier in the day, TOLO News, citing police, had reported that four people had died in the attack.
It was not immediately clear who was responsible for the terrorist attack. It came amid a three-day ceasefire offered by the Taliban militants in observance of the Eid al-Fitr holidays, following weeks of intensified violence across war-ravaged Afghanistan.
The Taliban and Afghan President Ashraf Ghani agreed on the truce to mark the end of the Muslim holy month of Ramadan after the militant group proposed it on Monday. It was only the fourth pause in fighting in nearly 20 years of conflict in Afghanistan.
However, despite the announcement of the ceasefire, about a dozen civilians were killed and several others wounded in four separate bombings across various parts of Afghanistan on Thursday.
The declaration of the ceasefire by the Taliban came two days after a massacre in Kabul, in which as many as 63 people, all students, were killed and 150 more were wounded in a bomb explosion that took place near Sayed-ul-Shuhada High School in the west of the capital.
Afghanistan’s Interior Ministry says at least 200 civilians have been killed and some 500 others injured in heightened Taliban violence since the beginning of the fasting month of Ramadan.
The Taliban have denied involvement in the acts of terror.
On Tuesday, the militants seized a key district near the capital.
The surge in violence came after the United States missed a May 1 deadline, agreed with the Taliban last year, to withdraw all of its troops from Afghanistan. Washington has pushed back the date to September 11.
While the Taliban have avoided engaging American forces, attacks against government and civilian targets have not stopped.
The US attacked Afghanistan in 2001, claiming that the Taliban were harboring al-Qaeda. The invasion removed a Taliban regime from power, but prompted widespread militancy and insecurity across the Asian country.