Libyan and US officials met face-to-face, but while Tripoli said it was seeking talks with no preconditions, Washington said it delivered a clear message: Col Muammar Gadafy must go.
The secret meeting occurred at the weekend as Libyan government forces fought rebels for control of the oil port of Brega, which the insurgents said yesterday 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 Gadafy 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 Ibrahim Moussa 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.
The rebels said they had routed most of Col Gadafy's troops in Brega, which has an oil refinery and terminal, and encircled it in a boost to their campaign after weeks of stalemate.
More than 40 people on both sides were reported killed in the fighting since late last week for a city which for months marked the eastern limit of Col Gadafy's control.
Rebel spokesman Shamsiddin Abdulmolah said its streets were strewn with landmines, making it hard to secure full control.
"The main body [of Gadafy's forces] retreated to Ras Lanuf," which lies to the west, he said by telephone from the eastern rebel stronghold of Benghazi.
The government denied the claim.
"Our brave soldiers are in Brega in their thousands and control it completely," spokesman Ibrahim said.
He said the government had lost 30 soldiers over five days of fighting, but rebels had lost many times more.
Abdulmolah said 12 rebels were killed and some 300 wounded on Saturday and Sunday. Most rebel forces were now past Brega and heading west.
Russia criticised the United States and others for recognising the rebel leadership as the legitimate government of Libya, saying they were taking sides.
Secretary of state Hillary Clinton announced US recognition of the rebels on Friday, a major diplomatic step that could unblock billions of dollars in frozen Libyan funds.
Brega has changed hands several times in the back-and-forth fighting along Libya's Mediterranean coast since the rebellion began in February.
Libyan TV, in a bid to counter the rebel claims, showed what it said was footage taken on Monday of ordinary life in Brega, with students taking an exam and workers at a natural gas plant.
Col Gadafy is refusing to step down despite the rebellion, Nato air strikes and defections of members of his inner circle.
On Saturday - as his envoys met US officials - he called rebels traitors and said he had no plans to leave the country.
The slow progress of the rebel campaign has caused strains in Nato, with some member states pressing for a negotiated solution to end a conflict many thought would last a few weeks.
Nato said it struck a military antenna radar system on Monday at Tripoli's main airport, but Libyan officials said it had purely civilian use.
On another front, in the Western Mountains region southwest of Tripoli, pro-Gadafy forces exchanged artillery fire on Sunday with rebels in the village of Al-Qawalish, a rebel fighter manning a checkpoint there told Reuters.
A rebel spokesman in the regional town of Zintan said rebels had repelled a bid by Gaddafi troops to enter the town.
Reuters