ZINTAN, Libya (AP) -- Opposition fighters in Libya's western mountains claimed control Thursday of the country's last functioning oil refinery, a blow to Moammar Gadhafi's regime in a week of stunning rebel advances that could turn the tide of the 6-month-old civil war.

The refinery is located in the strategic city of Zawiya, where rebels have made great strides in battles with government forces since their initial assault on Saturday.

"We have full control over the Zawiya oil refinery and we have liberated the whole city except two main streets," Col. Ali Ahrash told The Associated Press.

The BBC reported that one of its news crews were taken around the refinery by rebels and that there was no sign of pro-Gadhafi troops.

A rebel victory in Zawiya could leave Gadhafi nearly cornered in his increasingly isolated stronghold of Tripoli, the capital, just 30 miles (50 kilometers) to the east along the Mediterranean coast.

Rebel fighters are now closing in on the capital from the west and the south, while NATO controls the seas to the north. The opposition is in control of most of the eastern half of the country and has declared Benghazi, 620 miles (1,000 kilometers) east of Tripoli, as its de facto capital.

Ahrash, who was in Benghazi, said rebels have control of the cities of Surman, Sabratha and Zwara, as well as the road to Tunisia from Tripoli.

Families fleeing their homes to avoid a possible rebel assault on Tripoli described growing tensions and deteriorating living conditions in the capital: Security forces have blanketed the city with checkpoints, gun battles are heard after nightfall and power outages last days.

Five loud explosions shook the center of Tripoli on Thursday afternoon, possibly striking near Gadhafi's compound. NATO jets flew overhead minutes after the blasts. It wasn't immediately clear what was hit or if there were civilian casualties. NATO has bombarded military targets all over Libya since March when a no-fly zone was instituted.

The capture of the 120,000-barrel-per-day refinery in Zawiya is not expected to have a major impact on Gadhafi's ability to secure fuel.

The flow of crude to the refinery from fields in the southwest of Libya had largely been halted since midsummer. The refinery was believed to be running at about one-third of its normal capacity, drawing mainly on crude oil that was in its storage tanks. Zawiya mostly produced fuel oil, not gasoline.

Besides the seizure of the refinery, Ahrash told the AP that rebels were making progress in taking Zawiya, a city of 200,000 people.

He said Gadhafi troops were still in control of Gamal Abdel-Nasser Street and were hiding in the hospital there. Ahrash said Omar Mokhtar Street was still under Gadhafi forces control and that a few more troops were patrolling in eastern Zawiya.

Since the rebels entered Zawiya last week - their most dramatic advance yet after months of stalemate - Gadhafi's troops have been pounding homes, mosques and streets with rockets and mortar fire.

"In the past three days we have lost 70 fighters and more than 55 were injured," he said.

Libya's civil war began in February, with the rebels quickly wresting control of much of the eastern half of the country, as well as pockets in the west.

The conflict later settled into a stalemate with the rebels failing to budge the front lines in the east since April.

However, in recent weeks, rebels based in the western Nafusa mountains have advanced toward Gadhafi-held towns along the coast.

Back in Tripoli, Prime Minister al-Baghdadi Ali al-Mahmoudi said the government was in negotiations with rebels.

"We are also calling on all sides for a cease-fire," al-Mahmoudi said.

Gadhafi's government has previously called for a cease-fire, but continued to bomb towns where rebels tried to take power.

On a second front, hundreds of miles from Zawiya around the coastal town of Brega, rebels clashed with Gadhafi troops for control of that town's refinery.

Rebels control the two residential units in the oil terminal but have spent almost a week fighting for the refinery.

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Hatoum reported from Tripoli, Libya. Also contributing to this report were Rami al-Shaheibi in Benghazi and Hadeel al-Shalchi in Cairo.

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