The death toll in a car bombing targeting a bus in southwest Pakistan rose to 13 as police Friday arrested some two dozen suspects to investigate the attack.

The death toll in a car bombing targeting a bus in southwest Pakistan rose to 13 as police Friday arrested some two dozen suspects to investigate the attack, police said.

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

Police raided various parts of the city and rounded up some 24 suspects after the attack, an official told AFP, adding they are being investigated for any clues in connection to the bombing.

The banned extremist group Lashkar-e-Jhangvi (LJ) claimed responsibility for the killing in telephone calls to the local newspapers saying the "suicide attack" was carried out by them.

But police said 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.

Around 5,000 people have been killed in outbreaks of violence between different militant groups in Pakistan since the late 1980s.