Libyan rebels say they have seized the government's last functioning oil refinery in a city west of Tripoli, as they continue to push towards the capital in a bid to force leader Moammar Gadhafi from power.

The rebels said Thursday they were in control of the refinery in Zawiya, 50 kilometers west of Tripoli, a day after commanders said they shut down fuel lines leading to and from the facility.

Residents fleeing Zawiya said Wednesday opposition forces control most of the city, where their red, black and green flag can be seen. Pro-Gadhafi troops shelled it again Wednesday as snipers holed up at the refinery fired at rebel fighters.

The sprawling Zawiya complex provides only a small amount of the government's fuel oil, which Mr. Gadhafi has had smuggled in mainly from neighboring Tunisia and Algeria.

Clashes also continued on the eastern front in the strategic city Brega, where rebels said 18 of their fighters were killed and at least 33 wounded on Tuesday. Opposition forces are attempting to dislodge pro-Gadhafi troops from the oil port and refinery, which has not operated for months.

Meanwhile, the U.S. military has deployed two more armed Predator drones for surveillance operations over Libya, where opposition fighters remain heavily dependent on NATO air power.