Libyan and US officials have met face-to-face, with Tripoli seeking talks with no preconditions, but Washington saying it delivered the clear message that Muammar Gaddafi must go.

The face-to-face meeting occurred at the weekend as Libyan government forces fought rebels for control of the oil port of Brega, which insurgents said on Monday they now had surrounded in what would be a major boost to their campaign. Tripoli denied this.

The meeting was held "to deliver a clear and firm message that the only way to move forward is for Gaddafi to step down", a US State Department official said.

"This was not a negotiation. It was the delivery of a message." He said no more meetings were planned.

Libya said it welcomed discussions but only without preconditions.

"Any dialogue with the French, Americans, British is welcome," government spokesman Moussa Ibrahim told journalists in Tripoli. "We will discuss everything, but do not condition your peace talks. Let Libyans decide their future."

He said the meeting was in Tunisia on Saturday. The US official said it followed repeated contacts from the Libyan leader's emissaries.

France has also held similar talks with Libyan officials in the Tunisian resort of Djerba, insisting that Gaddafi must go into exile, the BBC reported.

"Clearly the situation is changing. If you had asked me 10 days ago I would have been more cautious," said French Defence Minister Gerard Longuet. "Clearly the situation is moving because Libyans of all origins are absolutely certain that Gaddafi is no longer an option for the future."

He said Gaddafi had to leave soon.

"The countdown has begun ... but I am cautious because Gaddafi is not rational and he could opt for a bunker strategy, taking the whole civilian population of Tripoli hostage."

UN Secretary-General Ban Ki-moon declined comment on the Libyan-US meeting, but said the world body was playing a central role in moves to present terms for Gaddafi to quit.

"There are many actors and the United Nations is playing a coordinating role. My special envoy is playing a central coordinating role," Ban told Reuters in Geneva on Tuesday.