Forces loyal to Muammar Gaddafi attacked the front gate of Libya's largest oil refinery near the coastal town of Ras Lanuf on Monday, killing 15 guards and wounding two, witnesses said.

"About 14 to 15 trucks came in from the direction of (Gaddafi-held) Sirte towards Ras Lanuf," said refinery worker Ramadan Abdel Qader, who was shot in the foot during the assault.

"We heard firing and shelling at around 9 in the morning from Gaddafi loyalists," he told Reuters.

A Reuters reporter saw the dead bodies of 15 men with gunshot wounds at a Ras Lanuf hospital where the injured were being treated. Blood covered the floor.

Qader said he and his colleagues had been sleeping when the pro-Gaddafi forces attacked the refinery.

The complex is controlled by Libya's National Transitional Council, the de facto rulers of the country after a six-month uprising ousted Gaddafi.

Called the "Ras Lanuf Factory for Production of Oil and Gas," the refinery was not fully operational but has a potential processing capacity of 220,000 barrels per day.

"It was Gaddafi militia -- maybe they were coming from the desert," Abdalil Salah, an official in the interim oil ministry told Reuters by telephone.

"There were some workers inside preparing and cleaning to get ready to start up."

About 60 staff were there when it was attacked, witnesses said.

"The aim of this attack was to scare the guards and the fighters and hinder the production of oil," said Mohamed el-Ferjany, an engineer at the refinery who was not present at the attack.

The interim prime minister said on Sunday that NTC-held facilities had begun producing oil, Libya's economic lifeblood, output of which had been all but halted throughout the war.

He did not say where production had restarted but promised that more of it would come online in the "near future".

Libyan oil firm the Arabian Gulf Oil Company (Agoco) said on Monday it has restarted production at the eastern oilfield of Sarir. Current output was 50,000 barrels per day, it said. – Reuters