DAMASCUS, Feb. 9 -- The US-backed Syrian Democratic Forces (SDF) thwarted an attack by the Islamic State (IS) militant group in eastern Syria, killing 10 assailants, a war monitor reported Saturday.

The IS sent 12 fighters to attack SDF positions near the al-Omar oil field in the eastern countryside of Deir al-Zour Province and the clashes lasted from midnight to the morning, said the Syrian Observatory for Human Rights.

The London-based watchdog said the SDF backed by US-led shelling foiled the IS attack.

The attack comes as the IS and the Kurdish-led SDF are negotiating about the fate of the last remaining IS militants in the eastern Euphrates river region in the eastern countryside of Deir al-Zour.

The SDF has been on a crushing offensive to root out the IS from the eastern Euphrates region since last September.

The SDF managed, with the help of the United States, to defeat the IS in much of the eastern Euphrates region.

According to the Observatory, more than 37,000 civilians, including dozens of IS militants, have fled the last IS-held pocket to areas controlled by the SDF in the eastern Euphrates region since last December.