Libyan rebels have begun an assault on an oil refinery in a city just west of Tripoli, in a bid to drive out forces loyal to Moammar Gadhafi and continue their advance toward the capital.

Rebels say they control most of the city of Zawiya, 50 kilometers from Tripoli. Its capture could allow them to cut a major supply route to the Gadhafi stronghold. While fighting raged at the oil refinery, reporters in Zawiya said most other parts of the city appeared deserted and quiet Wednesday.

Pro-Gadhafi forces shelled the area a day earlier. Libyan officials deny the rebels have taken control of Zawiya.

On Tuesday, Libyan rebels dismissed reports that they held talks with aides to the Libyan leader.

The head of the rebel Transitional National Council, Mustafa Abdel Jalil, said there have been no direct or indirect talks with Mr. Gadhafi's representatives, and that such talks are “unthinkable” unless the Libyan leader steps down.

Western news reports had said Mr. Gadhafi's aides met this week with Libyan rebels and U.N. envoy Abdul Ilah al-Khatib at a hotel on the Tunisian island of Djerba.

In Washington Tuesday, U.S. officials said Mr. Gadhafi's days are “numbered,” as rebels reported capturing towns to the south and west of Tripoli.