The Islamic State (ISIS) recently executed 10 boys no older than 12 years old after they attempted to escape from an ISIS training camp in Fallujah.

The jihadist group is also on the lookout for a 13-year-old boy who shot an undetermined number of ISIS fighters after they killed 70 pet birds he had been breeding.

Sources inside Fallujah disclosed that the ISIS had tried to stop the boy from breeding pigeons. When the boy persisted in raising the birds, ISIS militants came and killed all the birds, flogged the boy's father and slapped his mother when she tried to step in, Fox News reported.

"The boy was angered and he seized one of the fighters' AK-47 and shot them all," a witness said. 

Currently, the boy and his family are in hiding within their community, protected by family and neighbours who also despise the ISIS.

No other information was provided in the case of the 10 boys who were executed after fleeing the camp of the terror organisation.

Fallujah was reportedly the first prize claimed by ISIS in 2014. Sources who spoke by phone with Fox News painted a grim picture of life under an increasingly brutal and desperate ISIS, as it prepares for an expected assault by Iraqi government forces.

Baghdad has already liberated nearby Ramadi from ISIS earlier with the support from coalition forces and the Shia militias, but plans to retake Fallujah fell apart in the latter half of last year when the risk of civilian casualties was deemed too great.

"The Iraqi city is now a ghost town where fearful residents turn on one another and resistance is met with unspeakable brutality," according to sources trapped inside the Pittsburgh-sized community just 40 miles west of Baghdad, Fox News reported.

"They [ISIS militants] don Iraqi government uniforms to trick citizens into believing the liberation has begun, only to slaughter them when they venture from their homes. They also infiltrate local communities to root out disloyal residents. Hundreds are believed to have been killed trying to leave Fallujah, while those left behind suffer from food, water and electricity shortages,'' it said.

Unlike in normal schools, schools in Fallujah are open for only a few hours during the day. Boys and girls are strictly separated and the only courses being taught pertain to weapons use, a hard-line interpretation of Islamic doctrine and learning the classical Arabic language which differs from local dialects.

Under ISIS rule, Friday morning prayers are always followed by mass executions in the public square, including locking people in cages with ravenous wild animals, blowing them up, setting them on fire and driving armoured vehicles over them.

Women suspected of adultery are beheaded and men believed to be homosexual are thrown from atop buildings. Those who served in the Iraqi military or police force are hunted down and killed. Locals are stripped of their identity cards and documentations to deter further defection attempts.

The extremist group has sought from families to provide at least one or two child fighters – depending on the size of the family – and boys are forced to register for selection at age 14.

"They have had almost two years to build up the city for defences, make strong points, set all sorts of booby traps, dig tunnels for ease of movement between positions," said former U.S. Army Lt. Col. Daniel Davis, now a foreign policy analyst. "I'd expect they'd fight much more fanatically for Fallujah."