QUETTA: The death toll in a car bombing targeting a bus in Balochistan rose to 15 as police on Friday arrested some two dozen suspects to investigate the attack, police said.

Some 23 others were wounded in the bombing on a bus carrying Shia pilgrims returning from Iran on Thursday in the Hazar Ganji area on the outskirts of Quetta city, the capital of the oil and gas rich Balochistan province bordering Iran and Afghanistan.

Police had earlier put the death toll at 13.

“The death toll has risen to 15 as two more injured persons have succumbed to their wounds,” senior police official Hamid Shakeel told AFP.

Police raided various parts of the city and rounded up some 24 suspects after the attack, he said and added that they are being investigated for any clues in connection to the bombing.

The banned Sunni extremist group Lashkar-e-Jhangvi claimed responsibility for the killing in telephone calls to the local newspapers, saying the “suicide attack” was carried out by them.

But police said that they could not still confirm whether it was indeed a suicide attack.

“We are investigating this aspect also, but cannot confirm now that it was a suicide bombing,” Kakar said.

Markets were shut on Friday in Quetta after a strike call given by Shia leaders to mourn the deaths.

Balochistan has become an increasing flashpoint for sectarian violence between Pakistan's majority Sunni Muslims and minority Shia, who account for around a fifth of the country's population of over 170 million.