Meanwhile, Gaddafi forces fired a Scud missile, for the first time since the war began, from their central stronghold of Sirte, a US defence official said, adding that it had landed "harmlessly in the desert." "We think it was targeted at Brega," but was overshot by about 80 kilometres, the official said.
On Monday, sources close to the Tunisian security services reported talks had taken place in Djerba, near the border with Libya, as rebel forces drew closer to Tripoli and claimed to have cut vital supply lines to the capital.
But spokesman Farhan Haq said the United Nations had "no concrete information" on any talks in Tunisia and that its Libya envoy, Abdul Ilah al-Khatib, was not taking part in any such talks.
Khatib, who has spent months shuttling between Tripoli and Benghazi trying to kick-start ceasefire talks, had said negotiations on Libya's future would take place in a Tunis hotel and that he would attend.
The reports of rebel-regime negotiations sparked a swift denial from Benghazi, the insurgency's stronghold in eastern Libya.
"There are no negotiations or talks between the Gaddafi regime and the NTC in Tunisia or anywhere else," NTC Vice Chairman Abdel Hafiz Ghoga said.
In western Libya, Gaddafi forces shelled the centre of Zawiyah on Monday hours after rebels claimed they had seized control of most of the strategic port, according to an AFP reporter.