BEIRUT,— A US-backed Kurdish-led alliance forces pushed Thursday into the Islamic State group’s bastion city of Manbij in northern Syria, a monitoring group said.

Fighters of the Syrian Democratic Forces SDF managed to enter the city with support from air strikes by a US-led coalition, the Syrian Observatory for Human Rights said.

“The SDF entered Manbij from the south under cover of coalition air raids,” said Observatory chief Rami Abdel Rahman, whose Britain-based group relies on a broad network of sources inside Syria to monitor the country’s conflict.

He said there was “fierce street fighting between buildings” and that at least two SDF fighters had died when a bomb went off in a residential building.

Abdel Rahman said the SDF was able to break through IS defences a few hours after taking control of a village on the city’s southwestern outskirts.

He said progress was likely to be slow as SDF forces were facing booby-traps “planted by the jihadists to try to prevent the loss of the city.”

The SDF has faced fierce resistance from IS since launching the assault to take Manbij on May 31. It managed to encircle the city earlier this month but its advance slowed as IS fought back, including with almost daily suicide bombings.

The Kurdish-led Syrian Democratic Forces (SDF) is an alliance, formed in October 2015, from the Kurdish People’s Protection Units (YPG) with smaller Arab, Christian and Turkmen militias in a coalition intended to take on Islamic State.

The SDF has over 30,000 Kurdish fighters and about 5,000 Arab fighters.

The Kurdish YPG forces, which the U.S. and Russia consider an ally in the fight against Islamic State, are the most effective group fighting IS in Syria, as the Kurdish militia has seized swathes of Syria from Islamic State.

The jihadists have held the city since 2014, the year IS seized control of large parts of Syria and neighbouring Iraq and declared its “caliphate”.

Manbij, which had population of about 120,000 before the start of Syria’s civil war in 2011, is a key stop on IS’s supply route from the Turkish border to its de facto Syrian capital of Raqa.