Sickening new footage purports to show ISIS militants lining up and shooting 200 Syrian children, according to The Mirror. 

The video, circulated by an anti-ISIS activist, shows the children forced to lie face down side-by-side in the dust with around a dozen militants behind them with assault rifles and machine guns.

One armed militant then begins to open fire, shooting each child individually at point blank range. Others then join in, massacring the children on an industrial scale. It is not known why the children were executed although it is thought they were refugees fleeing violence.

The extremist group have become known for filming beheadings and other brutal executions of their enemies. However it is likely that these shootings, which last less than 30 seconds, are among ISIS' worst atrocities.

The terrorist group appear to be attempting to constantly invent more horrific means of execution. In addition to mass killings, public beheadings, dismemberment, running over with tanks and throwing people from tall buildings have all been methods employed by ISIS.

It is not the first time ISIS have explicitly targeted children. Last year in Iraq militants executed 1,700 military cadets over a period of a day and a half in Saddam Hussein's former presidential quarters.

This latest video, which has not yet been verified, has sparked horror and anger online. One commentator tweeted, "Beyond words...Shocking film shows jihadists massacring 200 Syrian children in mass execution." Another wrote: "This must be stopped! 200 Kids?!" Another called for western intervention, writing, "What will it take for the international community to take a hard stand against these guys? 200 children?"

Currently no western power has shown any indication of all out war on ISIS with America and Russia leading separate air-based campaigns in Syria and Iraq with Britain only targeting ISIS in Iraq.