A huge explosion has ripped through a crowded mosque in the Afghan capital Kabul, killing 21 people, police say.
Another 33 people were injured, Kabul police spokesman Khalid Zadran said.
Wednesday's blast occurred during evening prayers. The mosque's imam is reported to be among the dead.
It is unclear who was behind the attack, a week after a prominent so-called Islamic State (IS) militants killed a pro-Taliban cleric in a suicide bomb blast, also in Kabul.
IS has emerged as the most potent enemy of the Taliban, who seized control over Afghanistan last year. The two groups are now engaged in a murky and bloody battle.
Security forces have now sealed off the blast scene in Kabul.
Witnesses described hearing a powerful explosion which shattered windows in nearby buildings.
Stefano Sozza, the head of the Emergency NGO running the city's main hospital, told the BBC his group had treated 35 people, including children.
Intelligence teams said their investigation was ongoing.
IS focus seems to be widening
The mosque was crowded, the bomb powerful, and another cleric seems to have been in the sights of IS (Islamic State), the group which has emerged as the Taliban's most potent enemy.
In the past month, three prominent religious leaders were targeted in Kabul and there were assassinations in other cities.
Last week it was Sheikh Rahimullah Haqqani, known to be close to the Taliban. This time it's Amir Muhammad Kabuli, said to be an adherent of the more moderate Sufi faith.
Video posted on social media showed a scene of carnage.
One religious student who was just outside the mosque told the BBC he saw the bodies of the dead and injured sprawled inside, including children attending evening prayers.
IS's signature has been its devastating attacks on the minority Shia Hazara community. But their focus now seems to be widening just as the Taliban celebrate their one year in power - a takeover which ended one chapter of a long bloody war but only ushered in yet another.
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