A large explosion rocked a mosque in the Afghan capital during evening prayers on August 17, witnesses and officials said.
Afghan police said there were multiple casualties but could not yet give a tally.
One Taliban intelligence official told Reuters that as many as 35 people may have been wounded or killed, and the toll could rise further.
Al-Jazeera quoted an unidentified official as giving a death toll of 20.
Witnesses told Reuters the powerful explosion was heard in a northern Kabul neighborhood, shattering windows in nearby buildings. Ambulances rushed to the spot.
The Taliban intelligence official, speaking on condition of anonymity to Reuters, said the explosion occurred in a mosque among worshippers in the Khair Khana area of Kabul.
The imam of the mosque was among those killed and the toll could still rise, the source added.
Intelligence teams are at the blast site and investigations are ongoing.