The Britain-based Syrian Observatory for Human Rights, which relies on a network of activists on the ground, said that since the airstrikes began on September 23, 553 people have been killed, including 32 civilians. The civilians included six children and five women.
The group said it has documented the deaths of 464 fighters with the Islamic State of Iraq and Syria (ISIS) group, adding that the real number could be much higher. Another 57 fighters with the Al-Qaeda-linked Al-Nusra Front were killed in airstrikes on the northern province of Aleppo and Idlib, the Observatory said.
Many of the ISIS fighters have been killed in or near the northern Syrian town of Kobani, the target of a massive ISIS offensive since mid-September. ISIS fighters have captured dozens of Kurdish villages and forced more than 200,000 people to flee for safety in neighboring Turkey.
Earlier this week, US Central Command said its forces have conducted more than 135 airstrikes against Islamic State militants in and around Kobani, killing hundreds of fighters.
“Combined with continued resistance to [ISIS] on the ground, indications are that these strikes have slowed [ISIS] advances into the city, killed hundreds of their fighters and destroyed or damaged scores of pieces of [ISIS] combat equipment and fighting positions,” Central Command said in a statement.
An Associated Press journalist on the Turkish side of the border said heavy machine gun fire could be heard from the town on Thursday.
The Observatory meanwhile reported four coalition airstrikes on oil wells in the Jafra field in Deir Ezzor late Wednesday. The Local Coordination Committees, an activist group, also reported the airstrikes in areas held by ISIS.
The US-led coalition has aggressively targeted ISIS-held oil facilities in Syria, which provide a key source of income for the militants. But such strikes also endanger civilians, which could undermine long-term efforts to destroy the militant group.
The attacks on the oil industry, including refineries, have also led to a sharp rise in the price of oil products in rebel-held areas of Syria.