"This barbaric attack... is clear support to the Daesh terrorist organisation," said the Syrian Democratic Forces, who played a key part in retaking territory from IS last year, using an Arabic acronym for the jihadist group.

Turkey, which fears the prospect of a powerful Kurdish statelet taking root on its border, launched an operation against the Kurdish enclave of Afrin on Saturday.

The Kurds and other parties in the region have long accused Ankara of having abetted and supported the rise of IS, which swept across the region in 2014 and established a proto-state straddling Syria and Iraq.

The SDF, with backing from a US-led coalition's air power and special forces, led the battle that saw the jihadists lose their de facto capital of Raqa three months ago.

The Kurdish-led force now feels it is being poorly rewarded and, on the day the UN Security Council was due to discuss Turkey's Afrin offensive, urged the coalition to show support.

"The international coalition, our partner in the fight against terrorism with whom we jointly conducted honourable battles... knows full well this Turkish intervention comes to make final victory hollow," the SDF said in a statement.

The statement was read by SDF spokesman Keno Gabriel during a press conference in the northern Syrian town of Ain Issa.

"For this reason, the coalition is urged to take its responsibilities towards our forces and our people in Afrin," he said.