Muammar Gaddafi loyalists have swept into the opposition-held city closest to Tripoli, tightening security around the regime-held capital. To the east, rebel forces captured a key oil port as the country veered toward civil war.
Rebels said government forces had moved in to Zawiya, west of the capital, with tanks and dozens of people had been injured, but they vowed to keep up the fight. One rebel said the hospital was under control of pro-Gaddafi forces so the injured were being taken to a makeshift clinic set up in a mosque or to private homes for treatment.
"The number of people killed is so big. The number of the wounded is so big. The number of tanks that entered the city is big," he said. Opposition forces in the east, meanwhile, advanced west in a push toward Gaddafi's hometown of Sirte, a day after the port city of Ras Lanouf fell to the rebellion.
The contrasting fortunes of the two warring sides suggest that the conflict in Libya could last for weeks and maybe months, with neither side mustering enough military power to decisively defeat the other. The government is fighting fiercely to maintain its hold in Tripoli and surrounding areas and the rebels are pushing their front westward from their eastern stronghold.
Gaddafi, who has led the country virtually unchecked for four decades, has unleashed a violent crackdown against those seeking his exit, drawing international condemnation and sanctions. Hundreds have been killed, perhaps more, putting pressure on the international community to do more to stop the crackdown on protests that began on February 15, inspired by successful uprisings in Egypt and Tunisia, its neighbours to the east and west respectively.
The assault on Zawiya, a city of some 200,000 people just 30 miles west of Tripoli, began with a surprise dawn attack by pro-Gaddafi forces firing mortar shells and machine guns.
Witnesses said the shelling damaged government buildings and homes. The fighting sparked several fires, sending a cloud of heavy black smoke over the city, and witnesses said snipers were shooting at anybody on the streets, including residents who ventured onto balconies.
Initially, the rebels retreated to positions deeper in the city before they launched a counter-offensive in which they regained some of the lost territory, according to three residents and activists.
Pro-Gaddafi forces on foot and firing artillery, mortars and other heavy weapons launched a new attack on Zawiya late on Saturday afternoon from the south and west, two other witnesses said. The government claimed that "99%" of Zawiya was under its control.
The anti-Gaddafi rebels fared better elsewhere, capturing the key oil port of Ras Lanouf on Friday night, their first military victory in a potentially long and arduous march from the east of the country to Tripoli. Witnesses said Ras Lanouf, about 90 miles east of Sirte, fell to rebel hands after a fierce battle with pro-regime forces who later fled.