Libyan rebels battled their way back into a major oil port just 30 miles west of Tripoli, forcing Muammar Gaddafi's troops to close the vital coast highway and key supply route from Tunisia.
The renewed rebel offensive marked a significant rebound for opposition forces who were crushed and driven out of Zawiya nearly three months ago.
Rebels first took the city in early March, but were brutally expelled less than two weeks later in an assault by members of an elite brigade commanded by Colonel Gaddafi's son Khamis. That had left rebels with only tenuous footholds in Libya's far west.
Guma el-Gamaty, a London-based spokesman for the rebels' political leadership council, said opposition fighters had taken control of a large area on the western side of the city.
A rebel fighter who fled Zawiya at the end of March said "there are clashes inside Zawiya itself". The rebel, who identified himself only as Kamal, said "the fighters are back in the city" and that he had spoken with them.
While too early to mark a breakthrough in the stalemated civil war between Gaddafi forces and the rebels, who control roughly the eastern third of the country, an opposition offensive so near the capital was bound to put a nearly intolerable burden on forces loyal to the dictator.
They have been riddled by defections, badly hurt by ongoing UN-sanctioned Nato air strikes and facing huge resupply problems as a result of the naval blockade that has clamped off ports. The international actions are designed to help the four-month-old rebel uprising to drive Gaddafi from nearly 40 years in power in the oil-rich North African country.
Apparently prompted by the Zawiya clashes, Libyan soldiers sealed off parts of a crucial coastal road leading from Tripoli west to the Tunisian border.
An Associated Press reporter travelling the coastal highway approaching Zawiya from the capital reported it was clogged with soldiers and loyalist gunmen with assault rifles, some patrolling the road, others manning checkpoints. Roadside shops were shuttered. The only vehicles on the road were white jeep-style vehicles use by Gaddafi soldiers.
The coastal road is a key artery from neighbouring Tunisia for delivery for food, fuel and medicine for the Gaddafi regime.