Syrian rebels firing mortars and rocket-propelled grenades captured an oilfield in the country's east on Sunday after three days of fierce fighting with government troops protecting the facility, activists said.

The head of the U.K.-based Syrian Observatory for Human Rights, Rami Abdul-Rahman, said rebels overran the Al-Ward oilfield in the province of Deir al-Zour near the border with Iraq early on Sunday. About 40 soldiers were guarding the facility that the rebels had been pounding for the past three days, he said, adding that opposition fighters also captured several regime troops.

Oil was a major source of revenue for the cash-strapped regime of President Bashar Assad before the European Union and the United States imposed an embargo on Syria's crude exports last year to punish the government for its brutal crackdown on protesters early on in the uprising.

"This field used to supply the regime with fuel for its tanks and our aim was to stop these supplies," Omar Abu Leila, an activist in Deir el-Zour, told The Associated Press by telephone. He said there was heavy fighting recently near the oil facility that is located just east of the city of Mayadin.

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Abu Leila said that the oilfield had been functioning up until shortly before the rebels seized it. It was not clear whether the facility was damaged in the fighting or sabotaged by regime forces.

In the past year, Syrian officials have repeatedly accused rebel units of targeting the country's infrastructure, including blowing up the oil and gas pipelines in the energy-rich northeast of the country.

Syria exported some 150,000 barrels of oil a day before European and U.S. imposed sanctions took effect. In 2010, Syria earned $4.4 billion by selling oil to EU countries alone.

Talks in Qatar

Meanwhile, on Sunday hundreds of Syrian opposition politicians met in Doha to attempt to build a unified political and military front against President Bashar Assad's regime

The Qatar meetings, the opposition's largest since the uprising against the regime began in March 2011, are expected to run for four days.

The splintered opposition has recently come under fire from its key backer, the United States, which is pushing a proposal to revamp the Syrian National Council (SNC) and form a government-in-exile.

Under the proposal, called the Syrian National Initiative, a 50-member opposition group is to be created comprising members from the rebel Free Syrian Army as well as political groups inside and outside Syria.

The proposal was floated by Riad Seif, a prominent dissident who is seen as a favorite to lead a transitional government, opposition sources said.

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Seif, 66, told broadcaster Al Jazeera: "A priority of the transitional government, which is to result from the Doha meeting, is to topple Assad."

According to the proposal, the SNC would be included in the new entity, but with less influence.

"The council's members will attend the (Doha) conference to discuss the new initiative, but the council has not yet made a decision on it," Naji Tayyra, an SNC member, told dpa.

Since its formation in October 2011, the SNC has been plagued by infighting that has angered its Western backers.

The uprising against Assad started with peaceful demonstrations in March last year, but has since morphed into a bloody civil war. Activists say more than 36,000 people have been killed in 19 months of fighting.

At least 100 people were killed across the country on Sunday, reported the Syrian Observatory for Human Rights. A car bomb exploded near a major hotel in the Syrian capital of Damascus on Sunday, wounding several people, a pro-government television station reported. Damascus residents also reported clashes between Assad's forces and insurgents near a government security building in the district of al-Miysat. They said injuries were reported on both sides.

The opposition Syrian Observatory for Human Rights said that the rebels had shot down a warplane that was bombarding areas in the town of Deir al-Zour in eastern Syria. The pilot was captured, said the London-based group, citing local witnesses.