Foreigners make up the vast majority of the more than 140 jihadists killed by U.S.-led air strikes on the Islamic State group in Syria, a monitoring group said Thursday.

Jihadist fighters from Europe, Arab nations, Chechnya and Turkey dominated total the number of people killed, said the Britain-based Syrian Observatory for Human Rights.

At least 13 civilians have also been killed in the air strikes carried out by the United States and its Gulf Arab allies this week.

"A total of 84 Islamic State jihadists and 57 Al-Nusra Front fighters have been killed, among them just 12 Syrians," Observatory director Rami Abdel Rahman told AFP.

Al-Nusra Front is Syria's official Al-Qaida branch.

Abdel Rahman said that of the 12 Syrian fighters killed, 11 were members of the Islamic State group, and one was a member of Al-Nusra Front.

The United States and its allies -- including Saudi Arabia and the United Arab Emirates -- have carried out some 30 strikes on jihadist-held areas in northern and eastern Syria since Tuesday.