Pakistani police in southwestern Baluchistan province have arrested at least 11 people in connection with a deadly bomb blast on a passenger bus late Sunday.

The provincial police chief, Chaudhry Mohammed Yaqoob, says the suspects are all ethnic Baluch tribesmen and were arrested overnight in a series of raids in Quetta, the capital of Baluchistan province.

Local authorities say they have also taken the driver of the bus into custody for questioning.

Thirteen people were killed and 20 wounded when the bomb ripped through the bus carrying about 50 people from Quetta to the eastern city of Lahore.

No one claimed responsibility for the bomb. But the police chief blamed Baluch tribal militants who have stepped up their insurgency seeking greater autonomy and more compensation for the region's gas and other natural resources.

Some information for this report was provided by AFP and AP.