Israel is the only country in the world that Isis fears, according to the first Western journalist to enter the group’s territories and survive.
Jurgen Todenhofer spent 10 days in the so-called Islamic State last year, publishing his findings in a book.
In an interview with the Jewish News, the German reporter said Israel is not included in Isis’ planned “first stage” of colonisation in the Middle East.
“The only country Isis fears is Israel – they told me they know the Israeli army is too strong for them,” Mr Todenhofer said.
“They think they can defeat US and UK ground troops, who they say they have no experience in city guerrilla or terrorist strategies.
“But they know the Israelis are very tough as far as fighting against guerrillas and terrorists.”
The former politician said the Isis militants he met claimed not to be scared of British or American soldiers but believed the Israeli Defence Forces were “a real danger”.
Although Isis-affiliated groups are believed to be active in Gaza, no terror attacks in Israel and the Occupied Palestinian territories have yet been claimed by the organisation.
Mr Todenhofer described al-Qaeda as “peanuts” compared to Isis after being allowed to meet the group’s officials, militants and followers around its Iraqi stronghold of Mosul.