(Adds El Sharara field in paragraph 20, background)
By Ulf Laessing and Julia Payne
TRIPOLI/LONDON, March 5 (Reuters) - A North Korean-flagged oil tanker tried to dock at Libya's Es-Sider oil port seized by armed protesters who have threatened to sell oil independently unless they get political autonomy from Tripoli, Libyan officials said on Wednesday.
It was not immediately clear whether the Morning Glory tanker wanted to load oil when it approached the port on Tuesday, but any attempt to get crude to world markets independently would be an escalation of a blockade that has slashed Libya's vital oil exports.
State-owned National Oil Corp (NOC) has declared force majeure at the port and warned tankers against approaching because the Es-Sider terminal and two others in Libya's volatile east are under the control of heavily armed protesters.
Libya's government has tried to end a wave of protests at oil ports and fields across the North African country, which have slashed oil output, the country's lifeline, to a trickle.
There has been little progress in indirect talks between the Tripoli government and former militia leader Ibrahim Jathran, who seized the three eastern ports with thousands of men last year to demand political autonomy and a greater share of oil revenues.
It is extremely unusual for a North Korean-flagged oil tanker to operate in the Mediterranean region, according to shipping sources.
"The navy spotted a tanker from North Korea trying to enter Es-Sider port but it left," Libyan navy spokesman Ayoub Qassem said, confirming information from oil and shipping sources.
Control room workers at the port still loyal to the state oil company told the 30,000 tonnes-tanker not to dock because it did not have a contract with NOC, several oil officials said.
"The tanker came to Es-Sider but did not load oil," said an official at state-owned Waha Oil Co which operates the port and connecting oilfields.
An NOC official said he did not know whether Jathran's group had tried to attract buyers with the tanker but said: "We know they have been trying to sell oil."
STILL NEAR THE PORT
The vessel was still circling near the port on Wednesday, Reuters AIS Live ship tracking showed. It arrived in the area after sailing through the Suez Canal.
In January, the Libyan navy fired on a Maltese-flagged tanker which it said had tried to load oil from the protesters in the port.
An oil trader said it was almost impossible to track down the owner of a ship flagged in secretive North Korea.
Libya is struggling with armed groups and tribesmen who helped topple Muammar Gaddafi in 2011 but have kept their weapons to become political players and make financial demands.
An official in Jathran's group declined to comment. The group repeatedly said it might sell oil, bypassing Tripoli.
Jathran used to be a rebel fighter against Gaddafi and then commander of a government oil guard force until he defected last year, seizing the three ports which previously accounted for 600,000 barrels per day of exports.
He has teamed up with another set of protesters blocking oil exports at the 110,000-bpd Hariga port in Tobruk, also located in the east.
Libya's oil output has fallen to little over 200,000 bpd from 1.4 million bpd in July when protests started across the country, depriving the OPEC producer of its main budget source.
Western powers worry Libya will slide into instability as the government, paralyzed by political fights with parliament, struggles to assert control on a vast country awash with arms and militias.
Libya's defense minister held talks this week with protesters blocking the 340,000-bpd El Sharara oilfield in the south but NOC has not confirmed whether it will reopen soon.
The strikers, from a tribal minority, want national identity cards and a local council, demands the minister has promised to look into. (Additional reporting by Feras Bosalum; Editing by David Evans and Mohammad Zargham)