Supply lines to capital in peril as coastal cities fall amid US reports that regime has fired Scud missile near Brega

Muammar Gaddafi's regime has shown fresh signs of buckling as rebels have come close to cutting off supply routes and the Libyan interior minister arrived in Egypt in what appeared to be the highest-ranking defection for many months.

The Libyan leader broadcast a defiant appeal to his supporters to rid the country of "traitors", telling them: "The blood of martyrs is fuel for the battle." But the call was issued over a poor telephone line to state television, and most was inaudible – the result of what officials said was a technical breakdown.

Gaddafi's rallying call came as rebel fighters moved into Zawiyah, 30 miles west of Tripoli, straddling a critical road supply route from the Tunisian border. Rebel forces claimed to have near total control of the town, but government troops still held its oil refinery, the regime's last homegrown supply of fuel. Reuters reported that pro-government snipers in Zawiyah were firing on any civilians who ventured out of doors.

The anti-Gaddafi National Transitional Council (NTC) also claimed to have taken the city of Surman and said it was close to gaining control of Sabratha, along the same coastal road. A rebel spokesman said that talks were under way with government forces over their surrender.

There were clashes near the Ras Ajdir border crossing with Tunisia, and opposition forces were reported to be pushing towards Tripoli from the south having taken the strategic crossroads of Garyan over the weekend. Control of Garyan, in the Nafusah highlands, cuts off Tripoli from the Gaddafi stronghold of Sabha in the south. The multi-pronged offensive was an attempt by rebel commanders to cut off Tripoli's supply lines and regain the initiative after the killing of their military leader, General Abdul Fattah Younes.

With the pressure now on Gaddafi's forces, rebels in the formerly besieged stronghold of Misrata were able to relax for the first time in months.

"We feel good, things are moving," said Mohammed Elfeturi, 35, of the Faisal (Sword) brigade, alternately sipping his first coffee of the day and puffing his first cigarette. "We paid for it in blood."

Traffic was heavy on the intersection outside the makeshift coffee bar, no more than a small shop with some plastic tables and chairs arranged on the concrete outside. A few months ago, the area was a free-fire zone where rebels fought for their lives against government troops.

Gaddafi's Grad rockets no longer fall on Misrata, and the talk everywhere is of impending victory as news comes of advances in the west at Zawiyah, and in the east at Brega. Rebels pushed east from Misrata at the weekend, meeting light resistance, and say all that holds them back is fear of being hit by mistake by Nato jets.

AP reported that Gaddafi forces launched a Scud missile near Brega on Monday night, according to an unnamed US official, but that nobody was injured.

Fighting continues on the other side of the pocket, where rebels say government units, said to be commanded by Gaddafi's son Khamis, hold the town of Zlitan on the highway to Tripoli. But the fighters say the fight has gone out of their adversary.

"I think Nato did its job," said 20-year-old Farouk Mohammed, a veteran of five months' fighting. "They bombed his [Gaddafi's] weapons day after day."

British defence officials have also claimed that four months of relentless air strikes had fatally damaged the ability Gaddafi's forces to mount operations.

They indicated that the rebel seizure of Zawiyah signalled the beginning of the end in Libya. More than 7,000 Nato air strike sorties, some 700 of them British, had finally destroyed Libya's military machine, with Gaddafi's troops having to resort to pickup trucks, officials added.

In another blow to the regime's morale, the interior minister and longstanding Gaddafi security aide, Nasser al-Mabrouk Abdullah, arrived in Cairo via Tunisia in a private plane with nine family members. The minister reportedly told officials he was on holiday, and the Egyptian government said the minister had entered on a tourist visa. According to the AP, there were no Libyan diplomats at the airport to greet Abdullah and the embassy in Cairo had not been informed of his visit.

A Whitehall source said: "He has a reputation as a hardline Gaddafi loyalist with a long history in the security and intelligence agencies. If he is confirmed to have abandoned Gaddafi now, it is significant."

The UN special envoy for Libya, Abdel-Elah al-Khatib, was in Tunis on Monday, where a Tunisian government spokesman said he would meet "all the Libyan parties". But both Tripoli and the rebel council denied reports that their delegations were talking to each other in the Tunisian coastal town of Djerba.

"Why would we be talking to Gaddafi?" said Guma al-Gamaty, an NTC spokesman in London. "Right now, we have reached a tipping point, and he will probably fall in the next couple of weeks."

He said NTC forces would be careful to minimise the impact of their near siege of Tripoli on the citizen population, but he added: "The people know that whatever suffering there is in the short term will be worth it if it squeezes Gaddafi out."

A NTC statement issued on Monday called on people in Gaddafi-controlled area to organise themselves into "local committees to maintain security on the eve of the regime's downfall, and to raise awareness about the need for safeguarding public property, including universities, schools, hospitals, petrol stations, facilities and buildings, as they are the people's property, built with our own effort, sweat, money and sacrifice."