NATO was on Monday formally ending its Libya mission, which it has hailed as one of its "most successful" yet after its air strikes playing a key role in the overthrow of now-slain despot Moamer Kadhafi.

The no-fly zone and naval blockade, enforced by NATO since March 31, will end at 11:59 pm Libyan time (2159 GMT), as stipulated by a UN Security Council resolution last week that closed the mandate authorising military action.

NATO on Friday announced the end of the mission, declaring that the 28-nation alliance had fulfilled its UN mandate to protect civilians from a brutal repression.

"We have fully complied with the historic mandate of the United Nations to protect the people of Libya, to enforce the no-fly zone and the arms embargo," NATO Secretary General Anders Fogh Rasmussen said in a statement announcing the decision.

"Operation Unified Protector is one of the most successful in NATO history. We are concluding it in a considered and controlled manner -- because our military job is now done."

The mission was terminated even though Libyan interim leader Mustafa Abdel Jalil had asked for the alliance to stay until the end of the year, warning that Kadhafi loyalists still posed a threat.

But NATO deemed that civilians were safe from attacks after the new regime declared the country liberated following Kadhafi's death and the fall of his hometown of Sirte on October 20.

Western allies are now looking at how they can assist the new regime in Libya.

Rasmussen has offered that the alliance help the new Libyan leaders reform the country's defence and security institutions, but the military allies have repeatedly ruled out sending troops on the ground.

An alliance official said last week some allies could offer to provide the National Transitional Council (NTC) help in "air space management" and to control borders, but it would be outside the NATO umbrella.

Western strikes helped tip the balance of power in Libya's conflict, preventing Kadhafi from crushing a revolt that erupted in mid-February.

The bombing raids stopped Kadhafi forces from marching into the rebel eastern city of Benghazi in March and pulverised the strongman's air force.

The conflict then appeared headed into a stalemate as the ill-trained rebel forces struggled to fight their way west towards Tripoli. But with NATO destroying thousands of military targets, the NTC eventually took the capital in August, sending Kadhafi into hiding.

While NATO has steadfastly denied targeting Kadhafi during the campaign, it was an alliance air strike that hit his convoy as it fled Sirte, leading to his capture and killing on October 20. The alliance says it did not know he was in the convoy.

Facing global criticism over Kadhafi's death, the NTC vowed last week to bring Kadhafi's killers to justice in a sharp break with their previous insistence he was caught in the crossfire with his own loyalists.

A coalition led by the United States, France and Britain launched the first salvos in the air war on March 19, before handing over command of the mission to NATO on March 31.

The alliance, joined by Arab partners Qatar and United Arab Emirates, flew some 26,000 sorties and destroyed almost 6,000 targets during the conflict.