BENGHAZI, Libya, Aug 31 (Reuters) - At least two troops with Libyan commander Khalifa Haftar's forces were killed on Thursday when a car bomb exploded at a checkpoint in the area of Nawfiliya, a local witness said.

Haftar's Libyan National Army is one of the most powerful armed brigades in Libya, where rival factions and their military backers have competed for control since the fall of former leader Muammar Gaddafi in a 2011 uprising.

A LNA spokesman did not immediately respond to a request for confirmation.

Haftar's forces have been fighting against Islamist militants and other foes in eastern Benghazi and are besieging the city of Derna to oust militants there.

Nawfiliya is 80 km from Ras Lanuf, part of Libya's "Oil Crescent" and one the OPEC country's major oil exporting terminals. Libyan officials are concerned Islamic State may try to regroup there after defeat in nearby Sirte city last year.

(Reporting by Ayman Al Warfalli; writing by Patrick Markey, editing by Pritha Sarkar) ((pat.markey@thomsonreuters.com; +201069699524; Reuters Messaging: pat.markey.thomsonreuters.com@reuters.net))