ISIS is urging its members to plan for war with Iran and has ambitions to seize Tehran’s nuclear secrets, according to a manifesto attributed to one of its most senior members.

The document, typed on perforated sheets, is believed to have been written by Abdullah Ahmed al-Meshedani, a member of Isis’s highly secretive six-man war cabinet.

It was picked up by an Iraqi special forces unit during a raid in March on the home of one of the commanders of Isis, also known as Islamic State.

Thought to be a policy manifesto prepared for senior members of Isis, it is being examined by western security officials, who believe it to be authentic.

If so, it offers a unique insight into the ambitions of the Islamist