The US military formally ended operations in Sirte, where they partnered with forces loyal to Libya's UN-backed Government of National Accord (pictured) against IS jihadists
Tripoli (AFP) - Libya's UN-backed unity government has suffered a new setback after a political rival seized key offices in the capital and proclaimed the reinstatement of the former administration.
The United Nations' Libya envoy condemned the latest challenge to the authority of the Government of National Accord (GNA), warning it would sow "further disorder and insecurity".
The GNA is the centrepiece of Western hopes to stem an upsurge of jihadism in the North African nation and halt people trafficking across the Mediterranean that has led to thousands of drownings.
Led by prime minister designate Fayez al-Sarraj, it was intended to replace two rival administrations, one in Tripoli and one in the country's far east.
But late on Friday the head of the former Tripoli-based Government of National Salvation, Khalifa Ghweil, proclaimed its reinstatement from the offices of a key consultative body of the GNA.
His announcement added to the confusion surrounding the political situation in the oil-rich country, which is riven by power struggles and under the control of various militias who often switch allegiances.
The capital appeared calm on Saturday with no sign of any unusual military presence, including around the Council of State whose offices were stormed on Friday.
Ghweil has never accepted the legitimacy of the UN-backed government which took control of the administration in Tripoli in April.
But his position was severely weakened by the loss of support of militias in the capital after the UN deal.
Ghweil is subject to international sanctions, renewed by the European Union just last month.
In his statement, he declared all members of the GNA "suspended from their duties".
- 'Sole legitimate authority' -
The UN-backed government riposted with a statement threatening to arrest "those politicians who... attempt to create parallel institutions and destabilise the capital".
It condemned "efforts to sabotage the political agreement" brokered by the UN last December and denounced the seizure of the Council of State building by an "armed group".
UN envoy Martin Kobler expressed his "strong support" Saturday for the unity government as "the sole legitimate authority" under a UN-brokered power-sharing deal struck in December by some lawmakers from both sides.
US State Department deputy spokesman Mark Toner said Washington was "concerned" by the developments and urged restraint from all parties.
"Government buildings in Tripoli should be returned to the control of the Government of National Accord," he said, calling on "all parties to work together toward creating a safe, prosperous and free Libya."
A spokesperson for the European Union said: "The use of force to seize power in Libya can only lead to further disorder and a spiral of violence where the Libyan people would be the main victims."
The persistent chaos has hobbled Western efforts to battle a growing jihadist presence in Libya, which has been the launchpad of deadly attacks on holidaymakers in neighbouring Tunisia.
The authorities based in eastern Libya also refuse to cede power, bolstered by the backing of the well-armed militia of controversial military strongman Field Marshal Khalifa Haftar.
Libya has two rival parliaments, both elected since the NATO-backed overthrow of longtime dictator Moamer Kadhafi in 2011.
The first, elected in 2012, is dominated by Islamists and appointed the former Tripoli government.
The second, elected in 2014, appointed the administration in the east and has not formally endorsed the GNA.
But in February a majority of its members issued a statement expressing support for the UN-backed government.
Many of them said they had been coerced into not holding a formal vote of endorsement as stipulated under the UN plan.
In a careful balancing act, the UN plan made the 2014 parliament the sole legislative body, but also turned most of the members of the 2012 parliament into a mandatory consultative body, the Council of State.
The battle for power erupted into armed conflict last month when Haftar's forces seized all four of Libya's main eastern oil export ports.
He exploited the absence of fighters loyal to the UN-backed government who were battling IS in the city of Sirte to the west with air support from the United States.