ISIS genocide crimes must be investigated by the International Criminal Court, three European politicians urged in a letter this week.

The plea claimed the ICC did have jurisdiction to look into the atrocities because thousands of jihadist fighters came from countries under the court's watch. The letter to Prosecutor Ms Fatou Bensouda came after she refused to launch an examination into the group in April 2015, claiming the ICC could not begin proceedings under it had a referral from the United Nations Security Council.

A stalemate between Russia and the West means "it is extremely unlikely that the Council will refer the situations in Syria or Iraq to the Court", the letter said.

But it said several ISIS leaders come from countries including the UK, France, Germany and Belgium where the ICC does have jurisdiction and so does not need a referral.

The ICC was established under the Rome Statute and signatories of the treaty can be investigated for genocide, crimes against humanity, war crimes and crimes of aggression. Neither Syria or Iraq have signed the Statute so the ICC can only investigate if they are invited to by either nation or if they receive a referral by the UNSC.

The letter is signed by the Catholic peer Lord Alton of Liverpool, the Dutch politicians Dr Pieter Omtzigt and the Swedish MEP Lars Adaktusson. It says there are more than 5,000 ISIS fighters who come from European counties and so the ICC should launch its own investigation.

"Further delay in exercising existent jurisdiction only breeds impunity," they argue. "It would be proper, then, to begin preliminary examinations of atrocities committed by these foreign leaders and under their direction."

It insists that "extremely detailed and carefully researched" evidence has proved ISIS is "committing genocide against Christians and Yazidis".

It concludes: "We therefore call upon you, Madam Prosecutor, to initiate preliminary examinations into the atrocities against Christians, Yazidis, and other religious minorities in Syria and Iraq committed by foreign fighters acting on behalf of Daesh as you empowered to do so under the Rome Statute."

The letter comes after the Parliamentary Assembly of the Council of Europe (PACE) passed a resolution urging the ICC Prosecutor to recognize her jurisdiction over the perpetrators of genocide in Syria and Iraq as far as possible on October 12. 

Another co-signatory of the letter, Ewelina Ochab, Legal Counsel for ADF International, said: "The International Criminal Court must take action. The presence of thousands of European foreign fighters clearly places the ongoing genocide under the jurisdiction of the ICC Prosecutor. The impunity must end. Action must be taken before it is too late to save the remnant and before the evidence has been destroyed."