At least four people were killed after a loud explosion rocked a madressah located in Kuchlak area on the outskirts of Quetta, police said.

Twenty-two others were also wounded in the blast that took place after Friday prayers, Inspector General of Balochistan Police Mohsin Hassan Butt said. They were shifted to Civil Hospital Quetta.

The imam of the mosque inside the seminary, located 25km from the city of Quetta, was killed in the explosion, IG Butt told DawnNewsTV.

“The blast was carried out through a timed device that was planted under the wooden chair of the prayer leader,” said Quetta police chief Abdul Razzaq Cheema.

No group has claimed responsibility for the blast.

“The death toll could increase as some of the victims were seriously injured,” Shafqat Janjua, a police official, told Reuters.

TV footage showed the blast caused extensive damage to the walls and ceiling of the seminary.

This is the fourth explosion that has taken place 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 and 30 others were injured. The banned Tehreek-i-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.

The Balochistan cabinet had last month vowed to bring terrorists and their facilitators to justice and said that such attacks could not weaken the determination of the government against terrorists and their masters.