US-backed Kurdish-led fighters have seized ground from the ISIL group in Syria, a monitor said Tuesday, as the terrorists come under attack in their Fallujah bastion in neighboring Iraq.

US-backed Kurdish-led fighters have seized ground from the ISIL group in Syria, a monitor said Tuesday, as the terrorists come under attack in their Fallujah bastion in neighboring Iraq.

The so called "Syrian Democratic Forces", who control a swathe of territory along the Turkish border, launched a push south towards the ISIL stronghold of Raqa last week, capturing a string of villages in the north of Raqa province.

"The SDF has captured 12 villages... northwest of Raqa in the past 36 hours," Uk-based opposing Syrian Observatory chief Rami Abdel Rahman told AFP.

Abdel Rahman said that the villages lie 80 kilometers (50 miles) or more from Raqa itself but that the jihadists' de facto Syria capital was not the immediate goal.

He said the target of the offensive was the town of Tabqa and its adjacent dam on the Euphrates River, which lie some 40 kilometers (25 miles) upstream.

ISIL lost 18 fighters in the fighting on Monday, taking its losses since the start of offensive on May 24 to 79, he said.

The Observatory had no immediate word on SDF losses or any civilian deaths.

The United States has ignored angry protests from its NATO ally Turkey to back the SDF, an alliance of Kurdish and Arab fighters it regards as the most effective force on the ground against ISIL in Syria.

It has deployed more than 200 special forces personnel to work alongside it.

Ankara regards the alliance's most powerful component -- the Kurdish People's Protection Units (YPG) -- as a branch of the rebel Kurdistan Workers Party (PKK).

Foreign Minister Mevlut Cavusoglu said on Sunday that Ankara was ready to join forces with Washington for a special operation inside Syria on condition it did not involve the YPG.