US-backed Syrian fighters are pushing ahead in their offensive in northern Syria against members of the Islamic State group under the cover of U.S.-led coalition airstrikes.

The Britain-based Syrian Observatory for Human Rights says the fighting between Kurdish-led Syrian Democratic Forces and IS members on the eastern outskirts of the town of Tabqa left at least 11 extremists dead.

The SDF said on social media Monday that its fighters marched about 3 kilometers (2 miles) from the eastern side of Tabqa, the location of Syria's largest dam.

Last week, SDF fighters captured the area of Safsafeh east of Tabqa laying siege to the town.

On March 22, U.S. aircraft ferried forces behind militant lines in the Tabqa area to spearhead a major assault near the extremists' de facto capital, Raqqa.