Gunmen in Pakistan have ambushed a bus and killed 14 passengers after forcing them off the vehicle in the country's south-west, an official said.

Local official Jehangir Dashti said it was unclear who was behind the killings before dawn on Thursday.

He said about three dozen people were travelling to the south-western port of Gawadar when gunmen stopped the bus and killed 14 people after checking their identity cards.

The motive behind the killings is not known.

No group has yet claimed responsibility, but militant separatists and Islamist extremists are active in this part of southwest Pakistan.