NATO Wednesday extended its Libyan air war by three months and said the departure of strongman Muammar Gaddafi is only a question of time, as the African Union backed Russian mediation of the crisis.

Hours after NATO-led aircraft launched new raids on Tripoli, ambassadors of the military alliance meeting in Brussels decided to renew the mission for another 90 days to late September.

"This decision sends a clear message to the Gaddafi regime. We are determined to continue our operation to protect the people of Libya," said NATO Secretary General Anders Fogh Rasmussen.

"We will sustain our efforts to fulfil the United Nations mandate" to defend civilians from Gaddafi's forces, he said in a statement, adding: "We will keep up the pressure to see it through."

NATO, whose current campaign expires on 27 June, has intensified its air raids in recent weeks with daily strikes on command and control bunkers in Tripoli to prevent Gaddafi from crushing a revolt that began in mid-February.

Wednesday's decision would give individual nations time to prepare their contributions for the next 90 days, a NATO diplomat said.

"There were very positive signs that nations will extend with the appropriate number of resources," the diplomat said.

The Libyan government said Tuesday that the air war has so far cost the lives of 718 civilians and wounded more than 4,000.

"Since March 19, and up to May 26, there have been 718 martyrs among civilians and 4,067 wounded -- 433 of them seriously," government spokesman Mussa Ibrahim said, citing health ministry numbers which cannot be independently verified,

Ibrahim said these figures do not include Libyan military casualties, a toll the defence ministry refuses to divulge.

NATO cast doubt on the Libyan claim.

"We have no indications that that is the case," NATO deputy spokeswoman Carmen Romero told AFP, adding the alliance has no way to verify the claims because it does not have troops on the ground.

"NATO is conducting its operations to implement the UN mandate to protect civilians with great care and precision," she said. "This is in clear contrast with the indiscriminate attacks of the Gaddafi regime on his own people."

At a news conference in Tripoli, Ibrahim warned the departure of Libya's veteran leader, as demanded by NATO and the G8, would be a "worst case scenario" for the country.

"If Gaddafi goes, the security valve will disappear," he said.

"Gaddafi's departure would be the worst case scenario for Libya," he told reporters, and warned of "civil war."

But Rasmusssen told reporters in Brussels Gaddafi's departure is only a question of time.

"The question is not if Gaddafi will go but when," Rasmussen said. "It could take some time yet but it could also happen tomorrow."

Also in Brussels, the head of the African Union Commission voiced support Wednesday for Russian mediation of the Libyan crisis but insisted that Africa should remain a key player in finding a resolution.

"Anyone who can contribute to a resolution of the situation in Libya is welcome," said AU Commission chairman Jean Ping.

"If the Russians can help find a solution, they are welcome. We can't ask for anything better," Ping told a news conference after talks with European Commission president Jose Manuel Barroso.

Prodded by G8 partners at a summit in France last week, Russia, a critic of the NATO air war in Libya, agreed to act as a mediator in the conflict and openly called for Gaddafi to step down.

But Ping stressed that the AU cannot be marginalised in efforts to bring a political solution to the conflict, which began in mid-February when Gaddafi countered an uprising against his 41-year dictatorship.

"Libya is in Africa and we cannot find a solution by sidelining Africa," Ping said.

In London, The Guardian newspaper reported former members of Britain's Special Air Service (SAS) working for private security companies were in Misrata -- the main rebel-held city in western Libya -- advising the rebels and supplying information to NATO.

The former soldiers were gathering information about the location and movement of Gaddafi's troops and passing it on to NATO's command centre in Naples, military sources told The Guardian.

Defence ministry officials denied the private soldiers were being paid by the British government and insisted it had no combat troops on the ground.

The Maltese military meanwhile said that 76 boat people fleeing the conflict in Libya were rescued off the coast of Malta in a state of distress Wednesday after their vessel started taking in water.

The refugees were found adrift in their 15-metre boat and seemed to be in poor health. They told rescue workers a fellow migrant had died during the journey and his body had been cast into the sea, a Maltese military official told AFP.