Four rebel fighters were killed on Sunday when their positions west of the city of Misrata came under artillery fire from troops loyal to Libyan leader Muammar Gaddafi, a Reuters reporter said.

The reporter, at a field hospital near the front line, said he saw the dead and wounded being brought to the hospital in the backs of pick-up trucks.

"Gaddafi's army came forward about one kilometre (mile), they were trying to come to our side, and we are defending the position. That's why we are taking casualties," said rebel fighter Mohammed Ahmed.

He arrived at the field hospital with a wounded fellow fighter in the back of his armoured pick-up truck. The wounded man later died on the operating table, taking the death toll for the morning's fighting to two.

A short while later, another pick-up truck arrived with the bodies of a further two rebel fighters in the back, under blankets. Fighters and medical workers gathered around the truck and shouted "Allahu Akbar!", or "God is great!"

The rebels, who have been trying to push west from Misrata towards the government-controlled town of Zlitan, returned fire from multiple rocket launchers.