At least 28 civilians were killed by a U.S.-led coalition airstrike in Raqqah, according to local sources.

Coalition jets carried out massive airstrikes in the northern province on Friday, the sources, who spoke on condition of anonymity due to security fears, said.

Scores of people were reportedly injured in the raids.

Coalition airstrikes have killed a total of 484 civilians in the period from August 2014 to April of this year, according to the U.S. Central Command, which oversees combat operation in the Middle East and South Asia.

Local NGOs, however, estimate that more than 3,000 civilians had been killed by coalition airstrikes in both Syria and Iraq in the same period.

Syria has been locked in a vicious war since early 2011, when the Bashar al-Assad regime cracked down on pro-democracy protests -- which erupted as part of the Arab Spring uprisings -- with unexpected ferocity.

Since then, more than 500,000 people have been killed and more than 10 million displaced across the war-torn country, according to the UN.

AA