Muammar Gaddafi''s forces launched a fresh bombardment of the eastern Libyan oil town of Ras Lanuf on Thursday, rebels and witnesses said.

Bombs or missiles landed a few km (miles) from Ras Lanuf oil refinery and close to a building of the Libyan Emirates Oil Refinery Company building, a Reuters witness said.

"One bomb landed on a civilian house in Ras Lanuf," rebel fighter Izeddine Sheikhy told Reuters. He said the bombardment seemed to have come from the direction of the sea.

Reuters correspondents also saw an air strike from a plane over Ras Lanuf. Witnesses said it struck near the town''s eastern checkpoint. There were no immediate reports of casualties.

The front line has moved to-and-fro between Ras Lanuf and Bin Jawad, roughly 550 km (340 miles) east of Tripoli.

Rebel fighters said on Thursday they were based on the outskirts of Bin Jawad and near the oil complex of Es Sider, also known as Sidrah, which suffered a direct hit in Wednesday''s fighting, sending black smoke and flames belching into the sky. Es Sider came under intense bombardment by government forces again on Thursday.

That attack appeared to the be first on oil facilities, a move that has sent jitters through the oil market, stoking fears of a broader effort to destroy the OPEC producer''s capacity and infrastructure, and raising concerns of Middle East fall out.

Hassan Bulifa, a member of the board of east Libya''s Arabian Gulf Oil Co (Agoco), a unit of state oil firm National Oil Corp, told Reuters Agoco was arranging to market oil direct to foreign buyers instead of through its state-owned parent.

Rebels said there was heavy fighting reported around Bin Jawad on Thursday.

Earlier, rebels fired rockets out to sea after reports that Libyan gunboats in the Mediterranean were blamed for attacking rebel positions on the front line in the oil-producing east.

A counter-offensive by forces loyal to Gaddafi has halted the rebels'' advance along Libya''s eastern coast, where they have been forced to withdraw from the town of Bin Jawad.

"We came into Bin Jawad but gunboats fired on us so we withdrew," fighter Adel Yahya said on Wednesday night.

Rebels frustrated

Rebels, who have taken swathes of territory in the east and who are becoming better organised, have been stopped from taking the coastal road west to the prized target of Sirte, Gaddafi''s hometown, by tanks and warplanes.

In the push from Libya''s second city Benghazi, where the uprising started and where the rebels now have their headquarters, the rebel army of defectors and young volunteers has captured the oil towns of Brega and Ras Lanuf.

Rebels are frustrated a no-fly zone has not been imposed.

An American envoy left Cairo on Thursday on a plane to Salum on Egypt''s border with Libya, a Cairo airport official said. The official cited US embassy staff as saying he would be following Libyan developments at first hand.

Two US military planes arrived in Cairo from Jerba in Tunisia carrying 150 Egyptians who had been working in Libya, the airport official said. Three EgyptAir flights also arrived carrying 379 Egyptians.

The United States has sent planes in recent days to repatriate Egyptians after they fled to Tunisia from Libya.