Islamabad, Aug 16 (IANS): At least four people were killed and 22 injured when a bomb exploded inside a mosque after Friday prayers in Pakistan's Quetta city, the police said.

The explosion was carried out with an improvised explosive device (IED) which was placed inside the mosque in Kuli Qasim area of Kuchlak town, Geo News reported citing police officials.

The bomb was planted under the wooden chair of the prayer leader, said Quetta police chief Abdul Razzaq Cheema.

The imam of the mosque which is located 25 km from Quetta -- capital of Balochistan province -- was killed in the explosion, Inspector General of Balochistan Police Mohsin Hassan Butt told DawnNewsTV.

No group claimed responsibility for the blast.

This is the fourth explosion in Quetta over the past four weeks. On July 23, a blast had occurred in the Eastern Bypass area which left four people dead and 32 injured.

On July 30, another attack took place near a police station in which five people were killed. The Tehreek-e-Taliban Pakistan had claimed responsibility for that blast.

Last week, a man belonging to the Shia Hazara community was killed and 13 others wounded in a bomb explosion in a shoe market near Quetta's busy Meezan Chowk.