BEIRUT — 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 Britain-based Syrian Observatory for Human Rights, Rami Abdul-Rahman, said rebels overran the Al-Ward oilfield in the province of Deir el-Zour near the border with Iraq early 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 al-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.

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 European Union countries alone.

The uprising against Assad has 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.