The dreaded terror group Islamic State (ISIS) is planning a new coordinated attack across Europe, according to a former militant linked to the outfit.

The horrifying plan has been revealed after a former ISIS terrorist, identified only as Harry S, escaped the terror group and is now being questioned by authorities in Germany, the 'Daily Express' reported.

The German terrorist witnessed beheadings and executions in Syria for three months but fled after he could no longer stand its brutality.

"They want something that happens everywhere at the same time. All you need is to take a big knife, and go down to the streets and slighter every infidel you encounter," he has reportedly told his interrogators.

Harry S admitted he had been leading mass executions and holding weekly ideological training sessions in Raqqa, Syria.

In a video in May, he was spotted with the ISIS flag before other German-speaking militants called on supporters across the world to kill "infidels". The video ended with the militants shooting two prisoners dead, the newspaper reported.

Harry S now stands accused of membership of a terror group and faces a lengthy prison sentence if convicted.

IS has claimed responsibility for the November 13 Paris terror attacks which killed 129 people.