A massive suicide blast at a Shiite mosque in Kabul killed at least 27 people Monday and wounded 35 as worshippers gathered for a religious ceremony, officials said.
"It was a suicide bomber who blew himself up among worshippers inside the mosque, killing 27 and wounding 35," senior police official Fridon Obaidi said.
Police cordoned off the area around the Baqirul Olum mosque in the west of the Afghan capital.
"I was in the mosque, the people were offering prayers. Suddenly I heard a bang and windows broke. I had no idea what had happened. I rushed out screaming," Ali Jan told AFP.
Ashura commemorates the death of Imam Hussein, grandson of the Prophet Muhammad who was assassinated in the year 680.
His fate laid the foundation for the faith practised by the Shiite community, a minority in mainly Sunni Muslim Afghanistan.
Arbaeen marks the end of the mourning period over his death.
Earlier this year a powerful blast targeting Shiites during Ashura killed 14 people in northern Afghanistan. It came days after twin attacks claimed by Islamic State, which also targeted Shiites and killed 18 in Kabul.
No group has yet claimed responsibility for Monday's blast.