Pakistani police said a powerful bomb has gone off inside a mosque on the outskirts of the western city of Quetta during Friday prayers, killing at least four people and wounding 20.

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

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

Cheema added that the wounded were taken to nearby hospitals in Quetta, the capital of Balochistan province.

There was no immediate claim of responsibility, but Pakistani armed groups have been blamed for previous such attacks in Balochistan.

Balochistan, Pakistan’s largest and least populated province, is also rich in mineral and fuel resources. It has seen regular violence in recent years, with attacks claimed by Baloch separatists, Pakistan Taliban and local affiliates of the Islamic State of Iraq and the Levant (ISIL or ISIS) group.

Pakistan’s government claims it has quelled the rebellion, but violence has continued.

Balochistan is seeing a number of new infrastructure projects launched, including the port at Gwadar, as part of the $60bn China-Pakistan Economic Corridor (CPEC) project, a joint venture between the Pakistani and Chinese governments. (Agency report)