Child refugees fleeing ISIS in Syria (file(
Child refugees fleeing ISIS in Syria (file(Reuters

Islamic State (ISIS) jihadists are using civilians as human shields in the group's de facto Syria capital Raqqa, a Syrian activist said Tuesday, complicating things for a Kurdish-Arab alliance which has launched an offensive in the area.

The Syrian Democratic Forces, a seven-month-old alliance between Kurdish and Arab forces, launched an offensive on Tuesday in areas north of Raqqa.

The operation is potentially one of the most serious ground efforts against ISIS since it declared a self-styled "caliphate" straddling the Syrian-Iraqi border in 2014.

ISIS's use of human shields mimics tactics used by other Islamist terrorist groups, most notoriously by Hamas in Gaza during its war with Israel in 2014.

"They are using the civilians as a cover. So you'll find them in the same building. In a civilian building, you'll find two or three apartments for ISIS fighters," said Abdel Aziz al-Hamza, a co-founder of the Raqqa is Being Slaughtered Silently group.

"They also talk of some schools as places to stay because these schools have basements, something underground, so they are protected from the air strikes. And they are surrounded by civilian buildings."

There have been mounting concerns that the estimated 50,000 civilians believed to still be inside had nowhere to go.

"The civilians are besieged, they can't leave their city," said Hamza, who fled Raqqa in January 2014 and has been living in Germany.

"ISIS doesn't let anyone leave the city. At the same time, life has become at least ten times more expensive in the city," he said.

"They are trying to show all the time that their city is a paradise, and everything is okay and you can find whatever you want.

"You will find huge lines of thousands of people waiting to get some food and they are getting this food from a relief kitchen which is not supported by ISIS."  

The Syrian Observatory for Human Rights monitor said there had been intense coalition strikes in Raqqa on Tuesday, killing at least 22 jihadists.

According to US officials, several thousand ISIS jihadists are defending Raqa, while the SDF counts about 30,000 fighters.

AFP contributed to this report.