* UN urges Libyans to shun force to settle differences
* Protests planned as interim parliament's mandate runs out
* Demonstrations planned in capital, Benghazi in east
By Patrick Markey
TRIPOLI, Feb 7 (Reuters) - Libyan Prime Minister Ali Zeidan appealed for Libyans to avoid violence in settling a standoff over their interim parliament, whose mandate was due to run out on Friday with the country deeply divided over its future.
Two-and-a-half years since the fall of Muammar Gaddafi, Libya's democratic transition is in crisis, the government hamstrung by infighting between Islamists and nationalists and the nascent army is often unable to assert authority.
Militia in the east have blockaded oil exports - the country's main revenue lifeline and security remains a concern, highlighted by Zeidan's own abduction last October.
"I urge all citizens to be committed to peaceful means, all demands can be implemented peacefully and through dialogue," Zeidan said in a statement.
"The government is at the command of the people. We will implement the people's will no matter what it will be."
First elected in 2012, the General National Congress or GNC was supposed to end its term on Feb. 7. But its members have extended its mandate to allow a special committee time to draft the constitution seen as a key step in Libya's transition.
Many Libyans feel the GNC has made no progress with the legislature deadlocked between the nationalist National Forces Alliance (NFA), and the Justice and Construction Party (JCP), the political arm of the Muslim Brotherhood.
Two major Libyan rival former militia brigades - the Zintanis and the Misratans - are loosely allied respectively with the NFA and with the Islamist leadership.
Signalling its concern about political instability, the United Nations mission in Libya said in a statement that political leaders, revolutionaries and public leaders should prevent the use of violence "as a means of political pressure or resolving differences."
"Whatever the differences, safeguarding the legitimacy and avoiding disruptions of institutions are a national responsibility that rests with everyone," it said.
Protests against the extension of the GNC are planned in Tripoli's Martyrs' Square and in the eastern city of Benghazi later on Friday, with demonstrators expected to demand new elections or for a presidential committee to replace parliament.
Soldiers from the Libyan army barricaded off access to the GNC building and the road leading to the parliament.
Complicating Libya's transition, scores of brigades of former rebels who once fought against Gaddafi and refuse to disarm, have allied with competing political factions often using military muscle to pressure their demands.
One former rebel commander has occupied key oil ports in the east of the country, cutting off around half of Libya's oil export capacity to demand more autonomy and a greater share of petroleum wealth for his region.
Highlighting the tense security situation even in the capital, unidentified gunmen tried to storm the Libyan army's command headquarters in Tripoli on Thursday, exchanging gunfire with soldiers before stealing rifles and military vehicles .
(Additional reporting by Ghaith Shennib; Editing by Jon Boyle)