An oil tanker carrying 670,000 barrels of crude has left Libya's Ras Lanuf oil terminal, the first shipment since the port was reopened following a year of blockades by armed protesters, a spokesman for state-run National Oil Corporation said.

The tanker carrying Sirtica crude left the Libyan port on Tuesday evening, the spokesman said.

The shipment was a positive development for Libya's fragile central government, which is struggling to contain fighting between rival armed factions who have clashed with rockets and artillery for a month in Tripoli.

Until April, federalist rebels demanding more autonomy for their eastern region were holding four out of five eastern oil ports, cutting off over half of Libya's export capacity of 1.25 million barrels per day, and hitting production in the North African Opec member.

The government managed to strike a deal to free up the ports, but technical problems have delayed the full restart of shipments. The NOC says current national production is around 450,000 barrels per day.

The tanker leaving from Ras Lanuf, the Gemini Sun, was chartered by Austrian energy group OMV and was sailing towards Malta on Wednesday, Reuters AIS Live ship tracking showed.

OMV said on Tuesday its profits had been hard hit in the second quarter by lower output on Libya. It is now producing only 12,000 barrels per day in the North African country, little more than a third of the level before the toppling of Muammar Gaddafi three years ago. - Reuters