U.S.-backed Syrian forces made new territorial gains against Daesh on Saturday, moving closer to another of its major strongholds in northern Syria, according to the Syrian Observatory for Human Rights.The Observatory said the units from the Syria Democratic Forces (SDF), dominated by the Syrian PKK-affiliate Democratic Union Party (PYD) and People's Protection Units (YPG) militia, were now almost 17 km from the city of al-Bab, an Daesh stronghold north east of Aleppo.The SDF on Friday cut off the last route into the encircled town of Manbij from al-Bab after over a week of advances around that area, allowing it to lay siege to the large town from all directions, the monitor said..

The group, part of an alliance of Kurdish and Arab militias, launched an assault last week on Manbij after crossing the Euphrates River in Syria on Thursday, which Ankara warns is a redline and national security threat for Turkey.

The Observatory said nearly 160 Daesh terrorists had died in battles with the SDF around Manbij and more than 20 SDF fighters had been killed.The SDF, supported by U.S.-led air strikes and American special forces, launched an advance earlier this month to seize Daesh's last territory on the Syria-Turkey border.

The Observatory also said warplanes from a US-led coalition have been conducting heavy bombing raids on the town and its surroundings.

"Tens of thousands of civilians still there can't leave as all the routes out of town are cut," the Britain-based monitoring group's head Rami Abdel Rahman told AFP.

"Bakeries in the town haven't been open since Friday and food is beginning to become rare," Abdel Rahman said.