Displaced Iraqis who fled fighting between government forces and the Islamic State (ISIS) group in Anbar province line up to collect donated food at the Alexanzan camp in the Dora neighbourhood on the southern outskirts of Baghdad on May 31, 2106. Only a few hundred families have managed to slip out of Anbar's Fallujah area ahead of the assault on the city, with an estimated 50,000 civilians still trapped inside, sparking fears the jihadists could try to use them as human shields / AFP PHOTO / SABAH ARAR

At least 20,000 children are trapped in jihadist bastion Fallujah under siege by Iraqi forces and face shortages and forced recruitment as fighters, the UN Children’s Fund said on Wednesday.

“UNICEF estimates that at least 20,000 children remain trapped in the city,” the agency’s Iraq representative Peter Hawkins said.

The few residents who have managed to flee the Fallujah area since Iraqi forces launched an offensive against the Islamic State (ISIS) group on May 22-23 speak of severe shortages of food and drinking water.

The few hundred families who have escaped ISIS territory were camped out on the outskirts and residents reached by phone inside the city spoke of even worse conditions.

“Children face the risk of forced recruitment into the fighting, strict procedures for security screening and separation from their families,” Hawkins said.

“Children who are recruited see their lives and futures jeopardised as they are forced to carry and use arms, fighting in an adult war.”

UNICEF renewed calls for safe corridors to be opened to allow Fallujah’s civilian population to escape.

The United Nations has accused ISIS of using the civilian population as human shields as it prepares to mount a desperate defence of one of its most emblematic bastions.