TRIPOLI, Libya - Troops loyal to Libyan leader Muammar Gadhafi were fighting to retake the oil port of Ras Lanuf on Friday, intensifying their counteroffensive against the outgunned insurgents.

Government forces, with total air superiority and a big advantage in tanks, appear to have regained the momentum in the 3-week- old conflict and if their push proceeds apace it could overtake sluggish international efforts to halt Gadhafi.

The sound of explosions and small-arms fire came from Ras Lanuf on Friday as smoke rose from the town. Rebel forces said they were still inside the residential area of the oil port and fighting government tanks as well as troops who landed by boat.

"Four boats carrying 40 to 50 men each landed there. We are fighting them right now," rebel spokesman Mohammed al-Mughrabi said, but he declined to say exactly where he was.

Rebel fighter Ibrahim al-Alwani said he and his comrades were still in Ras Lanuf and had seen government troops in the town center. "I saw maybe 150 men and three tanks," he said. "I can hear clashes."

Insurgents withdrew their last main checkpoint in Ras Lanuf on Friday, setting it up 15-20 km to the east.

"This is our last checkpoint, ahead are clashes. The clashes are in the residential area (of Ras Lanuf)," rebel fighter Youssef Mohannad told Reuters at the checkpoint.

The insurgents were angry at the international inaction.

"Where is the West? How are they helping? What are they doing," shouted one angry fighter.

West of Tripoli, the revolt in Zawiyah appeared all but crushed, with insurgents clinging to only parts of the shattered city. Residents described scenes of carnage, with women and children among the dead.

One fighter said rebels had retaken the heart of Zawiyah from the army overnight, but authorities have kept journalists away from the town, about 50 km west of Tripoli.

Gadhafi's son Saif al-Islam told the rebels they faced a full-scale assault to crush their uprising which began after President Hosni Mubarak was overthrown in neighboring Egypt a month ago.

"It's time for action. We are moving now," he told Reuters in an interview on Thursday. He said the government had given the rebels two weeks for negotiations. "Time is out now."

As the military tide turned against the rebels, foreign powers held a flurry of meetings but remained at odds over whether or how to intervene to end the turmoil.

The insurgent leader warned that the delay could let Gadhafi regain control of Libya.

"We ask the international community to shoulder their responsibilities," Mustafa Abdel-Jalil, head of the National Libyan Council, told the BBC.