BEIRUT >> A rebel group with links to Al-Qaida captured Saturday an eastern Syrian oil field that is one of the country’s largest, activists said, a rare report of an opposition success in recent months that have been otherwise marked by government victories.

Also, a pro-government TV station said gunmen fired at a vehicle belonging to a Syrian Cabinet minister, killing his driver. The Al-Ekhbariya TV said minister Ali Haider was not in the car when it came under fire while traveling on a highway that links the central city of Hama with Tartous on the Mediterranean coast. A government media office confirmed the report.

Rami Abdurrahman, who is director of the Britain-based Syrian Observatory for Human Rights, said fighters from Jabhat al-Nusra captured the al-Omar field in the eastern Deir el-Zour province along the border with Iraq, ousting government troops during an overnight battle. There was no confirmation from President Bashar Assad’s government.

It was not clear if the field was operational. Before the uprising against Assad’s regime began in early 2011, the oil revenues provided around a quarter of the funds for the government budget. Since the revolt turned into a civil war over the past two years, exports have ground practically to a standstill, and Assad’s government has been forced to import refined fuel supplies to keep up with demand amid shortages and rising prices.

Oil revenues provided around a quarter of the funds for the government budget. In 2010, Syria was producing about 380,000 barrels a day and exports — mostly to Europe — bringing in more than $3 billion that year alone. Production now is likely about half that, experts estimate, given the rebels’ gains in oil-rich Deir el-Zour. The government has not released recent production figures.

Since late 2012, rebels have been seizing fields in Deir el-Zour, one of two main centers of oil production. In February, they captured the large Jbeysa oil field, after three days of fighting. A year ago, rebels briefly captured al-Omar field only to lose it to government troops days later.

Activists, including Abdurrahman, say rebels also control several of the small oil fields in the same area. It’s not clear how many oilfields altogether have fallen to the rebels, but experts and state media have previously said that most fields located along Syria’s border with Iraq are no longer under direct government control.

So far, the rebels have largely been unable to benefit from the oil fields, particularly since the country’s two refineries in the central city of Homs and the coastal city of Banias are in the hands of Assad’s troops. Regime warplanes’ control of the air makes it difficult for rebels to exploit the fields, as do the divisions among rival rebel factions.

Over the past year, the rebels have gained control of much of the territory in the country’s north along the border with Turkey, and in the east capturing dams on Euphrates River and army bases. In recent months, however, Assad’s troops have had the momentum, pushing rebel fighters out of a string of opposition strongholds around Damascus.

Earlier this week, the army also took two towns and a military base outside the northern city of Aleppo, Syria’s largest urban center, which has been carved up between government- and rebel-held areas since last year.

And on Tuesday, government troops captured the key town of Qara near the Lebanese border during an ongoing offensive in the mountainous western region of Syria. The operation is aimed at cutting off rebel supply lines to Lebanon and cementing Assad’s hold on a key corridor from the capital to the coastal area that is predominantly populated by Alawites, an offshoot sect of Shiite Islam that Assad also belongs to.

The Syrian conflict started as largely peaceful uprising against Assad’s rule in March 2011. It has morphed into a full-fledged civil war that has in the past year taken increasingly sectarian overtones. The rebel ranks are dominated by Sunni Muslims while the government and its armed forces are largely Alawite.

Christians and other minorities have tended to back Assad, and their villages have sometimes come under attack and places of worship damaged. It is not always clear if they are targeted for their religion or because of their strategic value. Rebels say some Christian villages have been used as artillery positions by government forces.

On Saturday, Syria’s main opposition group accused the army of deploying heavy weapons inside a historic Orthodox monastery north of Damascus. The Western-backed Syrian National Coalition said in a statement Assad’s army has turned the Cherubim Monastery into a base, shelling surrounding villages predominantly populated by Sunnis.

There was no way to independently confirm the information. Government officials could not immediately be reached for comment.