The meeting was scheduled for Saturday afternoon at a secret location in the eastern Libyan city of Surt.

In their first meeting the two men were to discuss a way of resolving the handover of two suspects in the 1988 Lockerbie boming.

Nick Pelham reports from Tripoli after being ordered off the Annan plane by Libyan authorities

Two-hundred-and-seventy people died when Pan Am flight 103 was blown up over the Scottish town of Lockerbie almost 10 years ago.

Earlier Mr Annan's flight met with an unexpected interruption when, on entering Libyan airspace heading for the eastern Libyan city of Surt, it was diverted to land in Tripoli.

Mr Annan was then asked to transfer to a Libyan passenger jet which took off for Surt - the Libyan seat of government 400 kilometres further east - leaving journalists behind.

Correspondents say the suprise re-scheduling shows just how unpredictable Kofi Annan's mission to Libya looks set to be.

Ten years on

Rob Watson: UN officials privately hopeful, but Annan could face resistance

In August, Britain and America offered a compromise arrangement under which the Libyan suspects would be tried in the Netherlands under Scottish law before a panel of Scottish judges. The incentive for Libya is to get UN Sanctions against the country lifted.

On his flight into Tripoli, Mr Annan told journalists that the discussions over resolving the Lockerbie dispute would be very difficult.

He said the UN had already given Libya answers to all the questions it had been seeking and that the deal was by no means sewn up.

Mr Annan said "God willing" he would be successful.

He goes to the meeting with backing from Western governments having received additional clarifications from the British Foreign Secretary Robin Cook on Friday.

Having not met Colonel Gaddafi before, Mr Annan said it would be an interesting moment and that he had no idea how the Libyan leader would react.

The BBC's UN correspondent says after years of stalemate there is some optimism that a solution may at last be in sight.

Fred Echkhard: "Mr Annan is hopeful of progress ..."

Fred Echkhard, spokesman for Mr Annan, told the BBC that the UN is "something of a middle man in this".

Privately, UN officials say most of the legal details have now been resolved and that arrangements are in place for the two suspects to be transported to the Netherlands if the meeting is successful.

But the US and Britain have made clear that negotiations over issues of substance, including the need for the two men to serve their sentences in Scotland if found guilty, are out of the question.

Dr Jim Swire: 'confident of justice', Ashoor Shamis: 'Gaddafi is sulking...'

The Libyan state news agency said yesterday that Colonel Gaddafi had no power to sign any deals with Mr Annan. The report has been interpreted as a sign that Libya may still want to delay a final solution.

But Dr Jim Swire, whose daughter was killed in the plane crash and has been leading the case for British families, said he was very positive about Saturday's meeting.

Key facts on Lockerbie
Profile: Muammar Gaddafi, Libyan maverick
Profile: Kofi Annan, Master of diplomacy