A U.S.-backed alliance has ousted Islamic State group jihadists from half of their Syrian bastion Raqa, a monitor said Wednesday, July 26, as the escalating fighting drove up the civilian death toll, AFP reports.

The Syrian Democratic Forces have been fighting for several months to capture the northern city, which has become infamous as the Syrian heart of IS's so-called "caliphate."

The SDF "are now in control of 50 percent of Raqa city despite the fierce resistance mounted by IS", Rami Abdel Rahman, head of the Syrian Observatory for Human Rights, told AFP.

The SDF assault has been backed by air strikes, special forces advisers, equipment and weapons from the US-led coalition fighting IS in Syria and neighbouring Iraq.

On Wednesday, a barrage of US-led air strikes across the city left at least 29 civilians dead, the British-based Observatory said.

"At least eight children are among the dead," Abdel Rahman said.

The SDF's Arab and Kurdish fighters first entered Raqa on June 6, seven months after launching their flagship offensive for the city -- called Operation Wrath of the Euphrates.

They have since steadily advanced in a pincer-like motion, closing in on the city centre.

But IS has fought back using a slew of car bombs, suicide attacks, weaponised drones and with improvised explosive devices scattered across the city.