BEIRUT -- Islamic State militants have carried out a deadly attack on U.S.-backed forces in Syria, killing and wounding many fighters and civilians, Syrian monitors and an IS-linked media outlet said Friday.
The assault took place on Thursday near the northern city of Raqqa, the Islamic State group's de facto capital, where U.S.-backed Syrian fighters are battling to rout the extremists from their stronghold.
The Syrian Democratic Forces have captured wide areas from IS in northern Syria since late last year, and on June 6, the U.S.-backed forces launched an offensive to capture the city of Raqqa. The fighting recently has been concentrated inside the city but IS staged Thursday's surprise attack on a village about 11 miles away from Raqqa.
The Aamaq news agency said the attack killed 53 SDF members and damaged two armored vehicles. It added that IS fighters returned to their base safely afterward.
Nisreen Abdullah, a spokeswoman with the U.S.-backed SDF, said IS has been carrying out attacks against the SDF but strongly denied the high number of casualties given by Aamaq.
"Daesh is trying to boost the morale of its fighters," Abdullah said by telephone from northern Syria, using the Arabic acronym for IS.
"Daesh is facing collapse," she added, referring to the loss of the group of almost half of Raqqa in the fighting so far in the city.
Rami Abdurrahman, who heads Britain-based Syrian Observatory for Human Rights, said IS fighters used motorcycles in the Thursday attack. He said they were able to kill and kidnap dozens of SDF fighters and civilians.
Meanwhile, near the Syrian capital of Damascus, members of an al-Qaida-linked group opened fire at protesters who demanded that the hard-liners leave the eastern suburbs known as eastern Ghouta.
Members of the powerful Hay'at Tahrir al Sham militant alliance -- Arabic for Levant Liberation Committee -- shot toward the protesters but did not cause any casualties among them, according to the Observatory and Ghouta-based activist Anas al-Dimashqi.
The al-Qaida faction is also known as HTS.
Al-Dimashqi said HTS fighters tried to tear down the tri-color flag of the Syrian uprising, adding that no one was hurt in the shooting. He said members of the Syrian rebel group known as Failaq al-Rahman protected the protesters.
Earlier Friday, the al-Qaida-linked HTS issued a statement saying the rebels shot dead a jihadi near his house in Ghouta and calling on Failaq al-Rahman to hand over those who shot and killed the fighter.