Eastern Libyan forces have said they would not allow the United Nations to use the only functioning airport in the capital Tripoli, hours after the UN Security Council passed a resolution demanding the warring parties commit to a "lasting ceasefire".

The self-styled Libya National Army (LNA) led by renegade military commander Khalifa Haftar has been trying to capture the capital city from the internationally recognised government since April.

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The UN earlier warned flight restrictions were hampering humanitarian and mediation efforts in the oil-producing country embroiled in a conflict between loose alliances from western and eastern Libya since 2014.

The LNA, which is backed by Egypt and the United Arab Emirates, has been trying since last April to take Tripoli but has failed to breach the city's defences.

However, it has air superiority thanks to UAE-supplied combat drones, which cover the whole of Libya via a satellite link, a UN report said in November.

LNA spokesman Ahmed Mismari told reporters in the eastern city of Benghazi that the UN would have to use other airports such as Misrata because it could not guarantee the safety of flights into Mitiga International Airport in Tripoli as Turkey was using it as a base.

Turkey has supplied combat drones to Tripoli operating in the past out of Mitiga and also sophisticated air defences for the capital.

The UN warned flight restrictions were hampering humanitarian and mediation efforts [File: Hani Amara/Reuters]

Security Council resolution

Late on Wednesday, the 15-member UN Security Council passed its first resolution on Libya since the Tripoli war broke out, expressing "grave concern over the exploitation of the conflict by terrorist and violent groups".

It demanded that the parties commit to a lasting ceasefire according to terms agreed by the country's Joint Military Commission, which has representation from the LNA and the internationally recognised Government of National Accord (GNA) based in Tripoli.

The resolution, which was drafted by the United Kingdom, was backed by 14 of the Council Members, with Russia abstaining. It expressed concern over the growing involvement of mercenaries in Libya.

David Schenker, the senior US diplomat for the Middle East and North Africa, told the US Senate Foreign Relations Committee the task of bringing the Libyans back to the negotiating table had been complicated by the involvement of external actors.

"Libya is not the place for Russian mercenaries, or fighters from Syria, Chad and Sudan. It is not the place for the Emiratis, Russians, or Turks to be fighting battles on the ground through intermediaries they sponsor or support," he said in prepared testimony.

The rival factions began UN-led talks in Geneva last week aimed at securing a ceasefire, but the first round of meetings failed to yield an agreement.

The resolution reaffirmed "support" for the UN mission in Libya (UNSMIL), which said earlier the LNA had in the past three weeks several times blocked UN flights carrying staff to and from Libya.

A humanitarian source said Haftar was imposing a "no-fly zone" for Tripoli and there were concerns that UN flights could be a possible target.

UN envoy Ghassan Salame has been mediating between Haftar and the Tripoli government.

Relations have been difficult as UNSMIL has condemned air raids blamed on the LNA, though mostly without mentioning the force by name.

Ties worsened when the UN said in a report last month that Haftar's main stronghold Benghazi had turned into a "hub for illicit economic activities, including the sale of drugs and arms". The UN also criticised teh activities of armed groups in western Libya.

The LNA's Mismari again accused Salame of being biased against the LNA, a charge denied by the UN.

UNSMIL has a base in Tripoli and also provides humanitarian relief for migrants and people displaced by the conflict with about 170 staff spread between Libya and neighbouring Tunisia.