Islamic State's English-language online magazine has claimed the group is holding an Israeli Arab for posing as a fighter in order to spy for Mossad.  

He is Muhammad Musallam, a Jerusalem resident.

Israel denies the claim and so does the man's father, Said Musallam. 

"My son went to Turkey for a vacation and he told me that he was kidnapped by ISIS in Syria. And that's it," he said.

The insurgents claim Musallam joined the group to report back to Israelis on its weapons stockpiles, bases and Palestinian recruits.

Musallam's mother, Um Ahmad, just doesn't believe her son would work for the Israelis. 

"Muhammad is a poor guy, he can't be doing that. Grant mercy for him, so God grants it for you too. My only wish from God is to protect him." 

Arabs make up 20 percent of Israel's population and the government has stepped up its monitoring of of would-be IS volunteers.