Libya: Fierce fighting in Brega further dampens talk of a cease-fire (UPDATES) (VIDEO)

Fierce fighting resumed in Libya on Sunday as rebels, backed by international air strikes, made incremental gains against Muammar Gaddafi's forces in the strategic oil town of Brega — about 500 miles east of the capital, Tripoli.

It was not immediately clear who controlled the city, which has changed hands six times in as many weeks. The country's vital coastal cities, however, now appeared evenly split between pro-Gaddafi forces controlling Tripoli and the west, and rebels controlling Benghazi in the east.

The rebels claimed to have recaptured Brega on Saturday, but pro-Gaddafi forces were said to be barricaded in the university and snipers were reportedly still active in the town that has been the scene of intense exchanges over the past few days.

"There is fighting going on inside Brega, Gaddafi's forces are based inside Brega university, and we're shelling them and advancing them bit by bit," a rebel commander named Col. Juma Abdel-Hamid told the Associated Press.

The U.S. and other countries contributing firepower to the no-fly zone have expressed ongoing concern about the lack of experience and discipline among the rebel fighters. But some veterans of the old Libyan army have reportedly joined the battle.

The rebels might be receiving some specialized training from U.S. and Egyptian forces, using weapons transported through Egypt, Al Jazeera reported, although the United States has denied the claim.

A rebel fighter and former teacher told Al Jazeera that he had received training in advanced weaponry from Egyptian and American "special forces" at a "secret facility" in the east.

He said he was supposed to learn how to fire advanced, heat-seeking rockets but was instead given a simple, unguided version of the rocket. The fighter, who asked to remain anonymous, also said Katyusha rockets had been sent into eastern Libya from Egypt.

While the CIA and British special forces are reportedly working with rebels on the ground in Libya, the U.S. Defense Department denied that its special forces were training Libyan rebels.

The development also raises questions about Egypt's possible covert involvement and whether the military leadership that has been in power since the ouster of Hosni Mubarak is breaking a U.N. arms embargo, Al Jazeera reported.

In Misurata, meanwhile, pro-government forces shelled a medical clinic Sunday killing one person and wounding 15 others, CNN reported. A doctor told CNN a 14-year-old child was one of those injured by successive mortar hits, suffering a fractured skull.

Misurata is Libya's third-largest city and the last major hold out for opposition fighters who have been resisting bombardment and attacks from Gaddafi's troops for weeks.

Medical officials told the AP that government forces had killed 37 civilians over the past two days and that an attack had burned down the city's main stocks of flour and sugar.

Gaddafi's forces have shelled the town of Yafran in a mountainous region south-west of Tripoli, Al Arabiya reported, quoting an eyewitness.

NATO, meanwhile, said it was investigating an air strike late on Friday that had targeted Gaddafi forces but instead hit several rebel vehicles, killing at least 13 fighters.

"NATO takes any reports of civilian casualties very seriously, but exact details are hard to verify as we have no reliable sources on the ground," Oana Lungescu, a NATO spokesperson, said, according to CNN.

A rebel spokesman, Shamsiddin Abdulmolah, told CNN: "Based on the information we have, they [the rebel forces] heard the air strikes and went ahead to see what the damage was, and that's when they got hit… They were told to stay back, but they jumped the gun."

Another report suggested that the mistake was caused by a rebel firing an anti-aircraft gun into the sky during a NATO sortie in the area, apparently in celebration after opposition forces advanced into Brega.

A spokeswoman for the so-called National Provisional Council, Iman Bugaighis, meanwhile has told the BBC the rebels are determined to improve their skills and fighting methods.

"We have reorganized our troops, our army forces. Now the army is in the front and then followed by our volunteers who are fighting with the army," she said. "We know and we admit that it's unequal forces of course, and we are, after all, civilians and volunteers, most of us; and it was planned, intentionally, from the beginning not to have [a] structured army.

"Of course we are determined, this is the end of it, that this land cannot bear both of us. We will do whatever it takes to liberate our country."

The possibility for a cease-fire has continuously faded since Friday, when a government spokesman, Musa Ibrahim, told reporters in Tripoli that rebels were not "really serious" about the offer, which he said included "silly conditions."

"They are asking us to withdraw from our own cities and open our cities to people, who are holding up arms, who are tribal, violent, no unified leadership, Al Qaeda links, and no one knows who they are. If this is not mad, then I don't know what it is," he said, according to CNN. "We will not leave our cities. We will not stop protecting our civilians."

Cease-fire conditions laid out by rebel leader Mustafa Abdul Jalil had included freedom of expression for the Libyan people and the removal of snipers and mercenaries from cities in the west. Ultimately, he said, the opposition's goal remained regime change in Libya.

Howevere, Abdel-Hafidh Ghoga, vice chairman of the National Provisional Council, sought to clarify the opposition's position Saturday. "There is no, and was no, negotiation on a cease-fire with Colonel Gaddafi's dictatorship," he said in a Benghazi.

In an interview with the AP, Ghoga said the council wanted to install a parliamentary democracy across the country and that any government established after Gaddafi's fall would reject all forms of terrorism and extremism.

"The Libyans as a whole, and I am one of them, want a civilian democracy, not dictatorship, not tribalism and not one based on violence or terrorism," he said.

Reports from Britain suggest, meanwhile, that Libya’s foreign minister — once dubbed the "torturer-in-chief" — has been offered asylum in the U.K. in return for his help overthrowing Gaddafi.

The Daily Mail reports that the secret offer was made to Musa Kusa while he was still in Tripoli and helped persuade him to seek sanctuary in Britain and is sure to provoke outrage.

Kusa has been linked with the Lockerbie bombing and the killing of British police officer Yvonne Fletcher outside the Libyan Embassy in London soon after the U.N.-sanctioned attacks began.

Kusa is being questioned by MI6 at a secret location in Britain while his wife and at least one of his children remain in Tripoli. He also reportedly has two daughters educated and living in the U.K. and a son who is a neurosurgeon working in the U.S.

— Freya Petersen