Russia and China are expected to show their support for Libya's interim government at a conference in Paris despite previously refusing to recognise the rebel council.
Delegates from Moscow and Beijing will join representatives from around 60 countries in Paris on Thursday for the biggest international conference on Libya since the uprising began in February.
The African Union, which withheld its support for the Libyan National Transitional Council (NTC) last week, will also be at the meeting. However a Whitehall source said it was not clear whether invitations sent to Brazil and South Africa, which had also refused, would be accepted.
Russia had called for Gaddafi to go but has remained critical of the Nato led-mission in Libya, as has China, which despite officially recognising the NTC has recently courted its officials.
Prime Minister David Cameron and French President Nicolas Sarkozy will co-chair Thursday's group, which is expected to discuss re-opening trade ties and setting a date for elections in a post-Gaddafi Libya.
A Whitehall source said: “The NTC is doing a remarkable job in tacking the problems of running the country, but they need a lot of support. The idea of Paris would be to demonstrate that support.”
The head of the NTC Abdel Mustafa Jalil will outline what help rebels need from the outside world. However the source stressed “this will not be a donor’s conference.”
The meeting comes as rebels prepare to close in on Gaddafi's hometown of Sirte, which remains a loyalist stronghold.
Leaders will also discuss a new UN resolution for Libya after 1973.
But in the two-hour conference world leaders may not be able to cover every issue in depth. The Whitehall source said the case of PC Yvonne Fletcher, who was murdered outside the Libyan embassy in 1984 may not come up.
“The French wanted to be respectful of the fact this is the Eid holiday, so we'll do what we can tomorrow and it'll no doubt set off a range of discussions which will no doubt be followed up”, the source added.
Separately the United Nations has unfrozen 1.8 bn Libyan Dinars – approximately £950m – which is being held in the UK. The money is scheduled to arrive in Benghazi on Wednesday evening.