Libyan rebels say they now control most of the strategic western town of Az-Zawiyah, as they continue an offensive aimed at isolating Tripoli, the country's capital.
The rebel push comes as Abdul Ilah al-Khatib, the United Nations' envoy on the Libyan conflict, arrived in Tunis, the Tunisian capital, where the country's foreign ministry said that he was due to meet with representives from Libya.
Both the United Nations and the Libyan rebel National Transitional Council in Benghazi denied that direct talks between the rebels and the Gaddafi government were taking place in Tunisia.
Meanwhile, Egyptian airport officials said Nassr al-Mabrouk Abdullah, the Libyan interior minister, had arrived in Cairo earlier on Monday, accompanied by his family members.
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The officials said the minister landed just before noon at the Cairo international airport, with nine members of his family.
They said he arrived on a special plane from Tunisia and told Egyptian officials that he was "on a tourist visit''.
The airport officials spoke on condition of anonymity because they are not authorised to talk to the media.
No officials from the Libyan embassy in Cairo were at the airport to greet the minister. Libyan officials were not immediately available for comment.
Meanwhile, a US defence official said Gaddafi's forces had fired a Scud missile for the first time since the uprising, but it landed in the desert and injured no one.
The missile was fired on Sunday morning from a location about 80 km east of Sirte, Gaddafi's home town, and landed east of the coastal oil town of Brega, the official said in Washington, speaking on condition of anonymity.
It was unclear what might have been its target, the official said.
In Az-Zawiyah, rebel commanders said they controlled most of the town, but that they were still taking sniper fire from forces loyal to Muammar Gaddafi, the Libyan leader.
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The rebel assault on Az-Zawiyah and its neighbouring towns began on Saturday, as they sought to cut off the southern coastal route from Tunisia which Gaddafi has been using to resupply.
Zeina Khodr, Al Jazeera's correspondent in Az-Zawiyah, reported that the rebels had taken control of a bridge along which the highway from Tripoli to Tunisia runs, but that central areas of the city remained contested, with Gaddafi forces employing snipers and mortar fire, as well Grad rockets.
On Sunday, Bashir Ahmed Ali, the rebels' battalion commander in Az-Zawiyah, said that his forces had suffered "many casualties" due to sniper fire.
He also told the AFP news agency that a tank and four fighters had been lost in a "friendly fire" air strike during the operation to take Az-Zawiyah.
On Monday, rebels said they were focusing on capturing or killing the snipers and clearing out any other pro-government forces left in the town.
The rebels have taken Az-Zawiyah twice before, only to lose it to government counter-offensives.
The opposition says it is being more cautious on this occasion. It arrested at least 15 people it alleged were mercenaries on Monday.
Almost all the shops in the town remained shuttered on Monday.
'Hundreds of volunteers'
The rebels say that they have also taken the towns of Surman, 60km west of Tripoli and Garyan, 50km to the south.
Moussa Ibrahim, the Libyan government's spokesman, acknowledged that there were "problems" in Surman, but said that "hundreds of volunteers" backed by the army were "handling the case".
He also acknowledged that the rebels had entered Garyan.
Clashes were also reported on Monday in the eastern oil town of Brega, where the rebels say they now control two-thirds of the town.
Al Jazeera's Tony Birtley, reporting from Brega, said that the town showed signs of intensive fighting having taken place, and that the rebels were continuing a push to take the oil terminal and industrial area.
The government denied on Sunday that rebel forces controlled any part of Brega.
Opposition forces hope that if they can take complete control of the city, its oil terminal and sea port will allow them to resume oil exports, and will give them a key staging area on the road to Sirte, a Gaddafi stronghold.
Gaddafi had earlier urged his supporters to fight for the country "inch by inch" in an audio message broadcast on state television with no images.
Facing the sternest challenge of his decades-long rule, Gaddafi called on Monday for Libyans to arm themselves to liberate the country from "traitors and from NATO".
The speech was the first time he had spoken in public since rebel fighters launched their biggest offensive in months.
"The Libyan people will remain and the Fateh revolution [which brought Gaddafi to power in 1969] will remain," Gaddafi said.
"Move forward, challenge, pick up your weapons, go to the fight for liberating Libya inch by inch from the traitors and from NATO.
"Get ready for the fight ... The blood of martyrs is fuel for the battlefield."
Source: Al Jazeera and agencies