"Unknown gunmen opened fire on five oil tankers parked at the roadside on the main Quetta-Jacobabad national highway in the Dasht area late Friday after which the vehicles caught fire," tribal police official Abdul Salam said.

There were no casualties, he added.

The tankers were waiting for a paramilitary and police escort for their onward journey to Afghanistan via the Chaman border.

No group has claimed responsibility.

Copyright AFP (Agence France-Presse), 2011