French President Nicolas Sarkozy and British Prime Minister David Cameron have arrived in Tripoli for a joint visit.
The two men are the first Western leaders to visit Libya since Muammar Gaddafi fled in August in the face of a massive rebel assault backed by NATO air strikes.
Cameron landed in Tripoli with Foreign Secretary William Hague but Sarkozy travelled separately, the Downing Street spokeswoman said.
A statement from Cameron's office said he would meet senior leadership of the National Transitional Council, including Libya's new interim leader Mustafa Abdel Jalil.
"He is expected to announce a further package of UK assistance to support the Libyan-led process of transition to a free, democratic and inclusive Libya," it said.
Britain and France were two of the first countries to launch military action over Libya, alongside the United States, in March to enforce a UN resolution to protect civilians from Kadhafi's forces.
NATO took over the campaign of aerial attacks a few days later.
The National Transitional Council were still battling Gaddafi loyalists in a swathe of territory from his hometown of Sirte on the Mediterranean coast through a string of Saharan oases towards the southern border.
A huge convoy of pickups mounted with heavy weapons massed on the coast west of Sirte early on Wednesday in readiness for what commanders said would be a pincer movement against the city, an AFP correspondent reported.
Half of the column massed at Tawurgha, south of Libya's third-largest city Misrata, would advance straight along the coast road, commanders said.
The other half would strike south into the desert towards the town of Waddan in the Al-Jufra oasis in a bid to cut Sirte off from Gaddafi's other principal bastion, the south's largest city Sabha, they added.
In a BBC interview ahead of the two European leaders' arrival, Abdel Jalil, promised that Tripoli had now been sufficiently secured since its capture from Gaddafi forces last month for the visit to go ahead.
"We say to the leaders coming tomorrow (Thursday) that they will be safe," he said.
AFP correspondents in the capital reported a massive security operation on Thursday with roadblocks along the road in from Metiga airport on the eastern outskirts and a luxury hotel in the city centre cordoned off by security forces backed up by French officers.
