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* Libya sees fiercest clashes since war against Gaddafi
* Shelling continues in Tripoli
* Benghazi battles involve troops, aircraft
BENGHAZI, Libya, July 24 (Reuters) - At least nine people were killed and 19 wounded, mostly civilians, in heavy clashes overnight in Benghazi as government forces tried to oust Islamist militants holed up in Libya's eastern port city, medical sources said on Thursday.
The fighting late on Wednesday involved aircraft and ground troops and followed more than a week of the fiercest clashes between militants, former rebel fighters and government forces in Benghazi and the capital Tripoli since the 2011 war against Muammar Gaddafi.
Sporadic shelling continued in parts of Tripoli early on Thursday though there were no immediate reports of any casualties after heavy clashes a day earlier.
More than 50 people have died so far in the violence that started ten days ago and that has deepened fears post-war Libya is slipping further into lawlessness, with its government unable to control heavily armed brigades of former rebel fighters battling for power.
Two main rival militias in Tripoli exchanged fire with Grad rockets, shells and anti-aircraft cannons for control of the main airport, shutting down most international flights and prompting the United Nations to pull its staff out of Libya.
Turkish foreign minister Ahmet Davutoglu said on Thursday Turkey may evacuate its embassy in Tripoli, a day after his ministry advised all Turkish citizens to leave the North African country due to the worsening security situation.
MILITIA BLOCKADES OF OIL INDUSTRY
The fighting has also taken a toll on Libya's fragile oil industry. The significant El-Feel oil field has reduced production due to the clashes and total output slipped around 20 percent to 450,000 barrels per day on Monday.
A spokesman for the state-run National Oil Corporation said on Thursday production had risen to 500,000 bpd, but he said there was still no progress on reopening the Brega oil port after a deal with protesters to end a blockade there.
Reopening Brega would help increase crude output by bringing the stalled Sirte oil operations back into production.
The North African OPEC oil producer's petroleum industry has been a prime target for blockades by militias and other armed groups looking to pressure the central government for financial or political gain.
Libya's western partners fear the country is becoming increasingly polarised between two main factions of competing militia brigades and their political allies, whose battle is shaping the country's transition.
One side is grouped around the western town of Zintan and their Tripoli allies who are loosely tied to the National Forces Alliance political movement in the parliament.
The other faction centres on the more Islamist-leaning Misrata brigades and allied militias who side with Justice and Construction Party, a wing of the Muslim Brotherhood.
Zintan fighters have controlled Tripoli airport since the fall of the capital in 2011, and have clashed with rivals repeatedly in the capital since the civil war. However, this week's battles were the most sustained since Gaddafi's fall.
Western powers hope the formation of a new parliament in August after a legislative election in June will open the way for the factions to forge a political settlement over the new government.
The previous parliament, known as the General National Congress, was caught up in deadlock between Islamist and nationalist factions, and blamed by many Libyans for their country's fragile progress to democracy. (Reporting by Ahmed Elumami; Writing by Patrick Markey,; Editing by Raissa Kasolowsky)