Dozens of other worshippers wounded in suicide attack in Paktia province
At least 20 killed at mosque in eastern Afghanistan
At least 20 people were killed and dozens wounded in an attack on a Shiite mosque in eastern Afghanistan during Friday prayers.
Officials have said they fear the death toll could rise after the assault, the latest targeting civilians who have borne the brunt of the violence in Afghanistan's long conflict.
"A suicide blast took place inside a Shiite mosque in the city of Gardez of Paktia province," said General Raz Mohammad Mandozai, police chief of Paktia near the Pakistan border.
"We have 20 people killed and around 50 others were wounded. All the victims were worshippers as they were busy offering Friday prayers when they were killed."
Gen Mandozai said at least two attackers opened fire on the crowd before detonating explosives.
Abdullah Hasrat, the spokesman for Paktia's governor, gave a slightly higher death toll of 22, warning that it could rise.
The head of Gardez's public health department Wilayat Khan Ahmadzai said that more than 70 people had been killed and wounded, with many rushed to the city's civilian hospital.
There was no immediate claim of responsibility for the attack.
It comes as urban areas across Afghanistan have been rocked by an increasing number of attacks in recent months, with both ISIS and Taliban insurgents targeting security forces and government installations.
The Taliban has not claimed a major attack in a city for weeks as it comes under increased pressure to agree to peace talks with the Afghan government.
But ISIS has carried out a number of attacks in the eastern city of Jalalabad and the capital Kabul in recent months, targeting everything from government ministries to a midwife training centre.
Last month an ISIS suicide bomber blew himself up near Kabul international airport, killing 23 people.
The increase in violence comes as US and Afghan forces intensify ground and air offensives against ISIS, and the Taliban step up their turf war with the group.
Earlier this week more than 150 ISIS fighters surrendered in a move that Afghan security forces and the Taliban hailed as the end of the extremist group in the north of the country.
Afghan civilians have borne the brunt of the war that began after the 2001 US-led invasion uprooted the Taliban regime.
Insurgent attacks and suicide bombs were the leading causes of civilian deaths in the first half of this year, a recent UN report said.
The total number of civilians killed was 1,692, the highest number for the period since the United Nations Assistance Mission in Afghanistan began keeping records in 2009.
Another 3,430 people were wounded.