The attack in Gardez, the capital of eastern Paktia province, also wounded dozens, officials say. No group has yet claimed responsibility for the attack.
At least 29 people were killed and more than 80 others wounded in the suicide attack on a Shia mosque in Paktia province, in eastern Afghanistan, Abdullah Hasrat, spokesman for the governor of Paktia province, said.
According to local authorities, there was at least one suicide attacker, possibly more.
The attack targeted a mosque in the provincial capital, Gardez, Hasrat said.
One witness said worshippers were praying when one man detonated his explosives. A second attacker is reported to have opened fire as worshippers gathered.
The mosque was packed with worshippers attending weekly prayers.
TRT World's Sultan Faizy, reporting from Afghanistan's capital Kabul, says officials suspect Daesh carried out the attack.
No group yet claims responsibility
No one has yet claimed responsibility for the attack, but the Daesh affiliate in Afghanistan has targeted Shia worshippers in the past.
Daesh has also warned Afghanistan's minority Shia that their houses of worship would be targeted.
Shia community often targeted
Afghanistan has mostly avoided the sectarian violence that has devastated countries such as Iraq, but there have been an increasing number of attacks on Shia targets in recent years.
No reliable census information exists on the size of the Shia community in Afghanistan, but estimates range around 10-20 percent of the country's 35 million population.
Most Shia are members of the Persian-speaking Hazara and Tajik ethnic groups.
Turkey condemns 'heinous' attack
"We learned with great sorrow that a terrorist attack which took place in a mosque today in Paktia province of Afghanistan resulted in many loss of lives and injuries," Turkey’s Foreign Ministry said in a statement.
"We strongly condemn this heinous terrorist attack targeting people worshipping."