(Adds Islamic State statement)

BENGHAZI, Libya, Jan 4 (Reuters) - Islamic State fighters clashed with a force guarding Libya's Es Sider oil export terminal on Monday, witnesses reported, and the militants said they had taken a nearby town.

The ultra-hardline group, which has taken advantage of years of chaos to grab territory in the Opec member, said in an online statement it had also set off a suicide car bomb during the clashes, causing casualties.

There was no one from Libya's authorities immediately available to comment on the reports of the fighting or the capture of Ben Jawad.

Es Sider and nearby Ras Lanuf oil ports, between Sirte and Benghazi on the Mediterranean coast, have been closed for more than a year amid fighting between rival factions for control of the North African state and its energy reserves.

Islamic State controls the city of Sirte and has attacked several oilfields in the south of Libya - though it has so far not taken control of any oil installations as it has done in Syria.

Libya has been split between rival governments, one based in Tripoli and the other in the east of the country, creating a security vacuum that militants have exploited.

Es Sider is protected by Ibrahim al-Jathran's Petrol Facilities Guard, an armed faction which has backed the internationally recognised government in the east, but is also in conflict with other forces supporting that government.

The United Nations has been trying to win support for a deal brokered in Morocco last month to create a national unity government for Libya.

Separately on Monday, a military plane that was targeting militant groups in the eastern Libyan city of Benghazi was shot down, though the pilot ejected, senior army commander Fadel al-Hassi told Reuters.

Military forces allied to the internationally recognised government based in the east have been battling militants based in the city for months.

(Reporting by Ayman Al-Warfalli; writing by Patrick Markey and Aidan Lewis; Editing by William Hardy and Andrew Heavens) ((pat.markey@thomsonreuters.com; +21620349006; Reuters Messaging: pat.markey.thomsonreuters.com@reuters.net))

Keywords: LIBYA SECURITY/PORT

* For a graphic, double click on http://reut.rs/1Y7VZoi

(Adds two guards killed, oil storage tank on fire)

BENGHAZI, Libya, Jan 4 (Reuters) - Islamic State fighters clashed with security forces near Libya's Es Sider oil export terminal on Monday killing two guards and setting an oil storage tank on fire, witnesses and a Petrol Facilities Guard source said.

The source told Reuters that the tank had been hit by a rocket during the fighting, causing a huge fire, and that two Islamic State suicide car bombers had attacked the area around the port after which its fighters had retreated.

According to Mohamed al-Manfi, an oil official based in eastern Libya, the tank was holding 420,000 barrels of oil.

Libya descended into chaos after the fall of Muammar Gaddafi in 2011 and rival governments and the militias that support them are fighting for control of the North African state and its energy reserves. Es Sider and nearby Ras Lanuf oil ports, between Sirte and Benghazi on coast, have been shut for a year.

Islamic State has taken advantage the security vacuum to grab territory and are threatening to advance from Sirte, which it controls. So far the group has failed to take control of any Libyan oil installations but has done so in Syria.

The group said it had attacked Es Sider after taking the nearby town of Ben Jawad. However, there was no independent confirmation of its capture.

Es Sider is protected by Ibrahim al-Jathran's Petrol Facilities Guard, which has backed the internationally recognised government based in the city of Benghazi in the east, but is also fighting other forces supporting that government.

The United Nations has been trying to win support for a deal brokered in Morocco last month to create a national unity government for Libya.

Separately on Monday, a plane targeting militant groups in the eastern city of Benghazi was shot down, though the pilot ejected, senior army commander Fadel al-Hassi told Reuters.

Militias allied to the Benghazi government have been battling insurgents based in the city for months.

(Reporting by Ayman Al-Warfalli; Writing by Patrick Markey and Aidan Lewis; Editing by Louise Ireland) ((Aidan.Lewis@thomsonreuters.com +216-58976557))

Keywords: LIBYA SECURITY/PORT