Benghazi: Muammar Gaddafi's forces put up unexpectedly fierce resistance on Monday, launching a deadly raid on an oil refinery far behind the front lines even as the ousted despot's son Saadi fled to Niger.

Southeast of Tripoli, civilians poured out of the desert town of Bani Walid after intense fighting on Sunday between Kadhafi loyalists holed up in the sprawling oasis and encircling new regime troops, according to reports.

NATO chief Anders Fogh Rasmussen vowed there would be no let-up in the alliance's bombing campaign against Gaddafi's remaining strongholds, which also include his hometown of Sirte and the southern oases of Waddan and Sabha, as long as his forces pose a threat.

The Gaddafi force killed 12 soldiers loyal to the new government in its attack on the oil refinery near Ras Lanuf on Libya's central coast, National Transitional Council military
spokesman Mohammed Zawawi said.

"So far, we have a figure of 12 dead in the ranks of the revolutionaries" guarding the key plant, Zawawi said after the attack deep behind NTC lines.

"A group (of loyalists) travelling in five vehicles tried to enter the refinery but were unable to," he said.

The oil infrastructure along the Mediterranean coast between Sidra and Brega was a key battleground of the seven-month uprising against Gaddafi and the front line between the mainly rebel-held east and mainly government-held west went back and forth several times.

But since the fall of Tripoli last month, NTC forces have advanced dozens of kilometres (miles) west towards Sirte, which remains in the hands of Gaddafi loyalists, and have
moved to secure the vital oil infrastructure on which its post-war reconstruction plans depend.

As civilians poured out of Bani Walid, many more residents remained trapped inside the town, 180 kilometres (110 miles) from the capital, for want of fuel for their vehicles, those fleeing said.

NTC fighters made little effort to check the identities of those passing through the checkpoints, the reports said.

"Families are scared to death by this war," said Mohammed Suleiman as he passed through with 10 relatives crammed into the back of his white BMW. Ezzedine Ramadan said the ferocity of Sunday's exchanges had prompted him to leave.

"Gaddafi's men were firing indiscriminately from the hills and rebels responded," he said as he drove through with his family. "We are expecting another attack on Monday, so we left," he

His wife Ibtissam said they had been forced to leave behind her brother.

"I am scared for those families stuck in the middle because there is no petrol," she said.

A medic at a field clinic outside Bani Walid said that at least 10 people had been killed in Sunday's exchanges.

"We received 10 killed and almost 20 injured, among them a woman with chest wounds," said surgeon Riba Ahmed.

In its latest update, NATO said warplanes under its command had hit 13 targets in and around Sirte, four around Waddan and one near Sabha.