The first Western reporter to be embedded with the Islamic State (IS, ISIS, ISIL) told ABC News that he came into contact with more than 14 American fighters during the 10 days he spent with the jihadist group.

According to German journalist Jürgen Todenhöfer, the American fighters come from different backgrounds — “both American born and Arab-Americans as well as white,” reports ABC News.

“I have seen many wars. That’s the strongest group I ever met. Very strong, very clever, very enthusiastic. They are extremely brutal. Not just head-cutting. I’m talking about the strategy of religious cleansing.” He elaborated, “That’s their official philosophy. They are talking about 500 million people who have to die,” he told ABC News.

“The guy from New Jersey. This surprised me,” Todenhöfer said, adding:

You don’t expect someone from N.J. going to join the Islamic State. … They were very tough, well informed. Some of them very successful in their own countries. In Iraq 30 percent are foreign fighters; in Syria 70 percent. They feel discriminated in their countries. They want to live in an Islamic state where no one can bother them and no one can discriminate against them. They are completely sure they will win this fight.

U.S. authorities have acknowledged that Americans have traveled overseas to join the Islamic State in Iraq and Syria, raising concerns about homegrown terrorist attacks carried out by these individuals once they return to the United States.

FBI Director James Comey told Breitbart Texas in August:

While the organization currently operates in the Middle East, the group has foreign members who might be able to travel into Europe and possibly into America. That is why the FBI has been working to monitor any attempts of such travel as well as their efforts to recruit individuals in the United States.

A U.S.-led international coalition has been conducting constant airstrikes against ISIS in Iraq since August. President Obama expanded the U.S. war against ISIS into Syria the following month.