The explosion, which witnesses said collapsed the mosque's roof, took place in eastern Nangarhar province in Afghanistan.
At least 62 worshippers were killed and more than 100 were wounded by a blast inside an Afghan mosque during Friday prayers, officials said, a day after the United Nations said violence in the country had reached "unacceptable" levels.
The explosion, which witnesses said collapsed the mosque's roof, took place in eastern Nangarhar province, provincial governor spokesman Attaullah Khogyani told AFP.
Afghan officials have yet to determine whether the 'two' reported blasts were due to a planted explosive device, rocket or mortar attack.
He said the dead were "all worshippers" in the blast in Haska Mina district, roughly 50 kilometres (30 miles) from the provincial capital Jalalabad.
There was no immediate claim of responsibility. Both the Taliban and the Daesh group are active in Nangarhar province.
Sohrab Qaderi, a member of the provincial council in Nangarhar, while expecting a rise in the number of casualties, said that more than 100 others had been wounded.
Malik Mohammadi Gul Shinwari, a tribal elder from the area, said that the mosque had completely collapsed.
"It was a heartbreaking scene I witnessed with my eyes," Shinwari said, adding that 32 bodies and scores of injured have been transported from the blast site.
Tezab Khan, a member of the local police who was on duty in the area, said: "I could hear the Mullah who was preaching and suddenly his voice was silenced with a boom,"
"When I arrived on the scene, people were trying to bring out the bodies and injured who were stuck under the fallen roof."
The blast came after the UN released a new report on Thursday saying an "unprecedented" number of civilians were killed or wounded in Afghanistan from July to September.
The report, which also charts violence throughout 2019 so far, underscores how "Afghans have been exposed to extreme levels of violence for many years" despite promises by all sides to "prevent and mitigate harm to civilians."
It also noted the absurdity of the ever-increasing price paid by civilians given the widespread belief that the war in Afghanistan cannot be won by either side.
"Civilian casualties are totally unacceptable," said the UN's special representative in Afghanistan, Tadamichi Yamamoto, adding they demonstrate the importance of talks leading to a ceasefire and a permanent political settlement.
The figures — 1,174 deaths and 3,139 injured from July 1 until September 30 — represent a 42 percent increase compared to the same time period last year.
The UN laid most of the blame for the spike at the feet of "anti-government elements" such as the Taliban, which has been carrying out a bloody insurgency in Afghanistan for more than 18 years.
July alone saw more casualties than in any other month on record since the United Nations Assistance Mission in Afghanistan (UNAMA) began documenting the violence in 2009.
Khogyani said the victims include children who were at the mosque, and that the number of casualties could still rise.
Over the last two months the tenacious spate of bloody violence in Afghanistan has claimed more than 3,000 lives on all sides, including the time around September's landmark presidential polls.
Afghanistan has seen a new high in Taliban-claimed bombings and coordinated group assaults as well as aggressive air and ground operations by Afghan and US forces amid the failure of peace talks.
No one immediately claimed responsibility for the mosque attack, but both the Taliban and the Daesh terror group are active in eastern Afghanistan, especially Nangarhar province.
On Thursday, a UN report said more than 2,500 civilians were killed and over 5,600 wounded in the first nine months of this year.