Smoke rose after a U.S.-led air strike in the Syrian town of Kobani, Oct. 8, 2014. Reuters

A United States-led air campaign has killed at least 2,000 people in Syria since September, a monitoring group said Thursday. Most of the 2,000 killed most have been Islamic State jihadists. "At least 1,922 fighters from IS, mostly foreigners, have been killed since September 23, 2014 in raids and aerial attacks by the international coalition on IS positions and oil refineries," across Syria reported the Syrian Observatory for Human Rights said, Agence France-Presse reported.

The monitoring group also reported that that 66 civilians, including 10 children, have been killed in the U.S.-led airstikes. Ninety fighters from Al-Qaeda Syrian affiliate Al-Nusra Front have also been killed in the coalition attacks, the Britain-based monitoring group said, via the Times of Israel.

The air strikes on oil refineries might hamper ISIS's financial abilities, while also targeting jihadists. A BBC documentary Wednesday night said that the Islamic State is selling seized Syrian oil back to Syrian President Bashar Assad’s government for cash. The documentary also reported that the Islamic State has about $2 billion at its disposal, earned mainly through the seized oil fields.

The air strikes have focused on the country's central province of Homs, Aleppo in the North, Hasakeh in the Northeast and Deir Ezzor to the east, as well as the province of Raqa, known as the center of the Islamic State.

A recent U.S.-led airstrike was rumored to have injured Abu Bakr al-Baghdadi, the leader of the Islamic State. The BBC and the Guardian reported Tuesday -- citing a Western diplomat and Iraqi advisor -- that al-Baghdadi had been seriously injured in a March 18 airstrike that hit a convoy of vehicles between the Iraqi villages of Umm al-Rous and al-Qaraan close to the Syrian border. US officials were quick to shoot down the reports however.

“We have no reason to believe it was Baghdadi,” Pentagon spokesman Col. Steve Warren told the Daily Beast on Tuesday. The Guardian reported, however, that the injuries to Baghdadi were serious enough that ISIS was preparing to have no name a new leader.