At least 18 people, including a key cleric Mawlawi Mujib Rahman Ansari, were killed, and 23 others injured by an explosion outside a mosque in Afghanistan's Herat City on Friday, local media reported, citing the governor's spokesperson.

"Mujib Rahman Ansari, with some of his guards and civilians, have been killed on their way toward the mosque," said Herat's police spokesperson Mahmood Rasoli.

The reason for the explosion is not yet known.