An attack on a Shi'ite mosque in the western Afghan city of Herat on Tuesday killed more than 20 people and wounded 30 others, officials said.

Hospital authorities in Herat said all the dead and wounded were worshipping in the mosque when a suicide bomber blew himself up.

Abdulhai Walizada, a local police spokesman, said there appeared to be more than one attacker, with a suicide bomber who detonated explosives and another who threw grenades at worshippers.

There was no immediate claim of responsibility for the latest attack to hit Afghanistan, which has seen more than 1,700 civilian deaths so far this year.

Afghanistan has traditionally been relatively free of the sectarian violence common in Iraq or Syria but hardline Sunni militants from the local branch of Islamic State have repeatedly attacked the mainly Shi'ite Hazara minority in the past year. (Reporting by Jalil Rezaee and Hamid Shalizi