ZAWIYA, Libya — Rebels battled Moammar Gadhafi loyalists today for control over Libya’s only functioning oil refinery in the western city of Zawiya as the opposition tried to cut off fuel supplies to the regime’s stronghold of Tripoli.

Rebel fighter Ramadan Keshada said his forces control parts of the refinery complex in the city’s north on the Mediterranean coast, while some regime troops and civilian workers remain inside. He said rebels and regime forces clashed there on Tuesday, then the opposition fighters pulled out at nightfall and made a new push in the daylight.

The Libyan rebels made a dramatic advance over the weekend out of their bases in the western mountains near the border with Tunisia into Zawiya, just 30 miles from the capital Tripoli. They took control of parts of the city but have been fighting fierce battles with Gadhafi’s forces to hold their ground and take more territory.

The rebel advance is tightening the noose around Tripoli.

The fighters are closing in on the capital from the west and the south, while NATO controls the seas off Tripoli, which sits on the Mediterranean coast.

Hundreds of miles away from the capital, the opposition is in control of most of the eastern half of the country, and have a transitional leadership council in their de facto capital of Benghazi.