10 Americans fighting with IS

The Pentagon announced that about 100 American fighting alongside extremist organizations, including ten with the Islamic State (IS).
Pentagon's spokesman, Lt. Col. Steven Warren in a news conference: "We believe that about one hundred American citizen currently are fighting in Syria, we do not know precisely the organizations to which they belong, and we believe that ten Americans are fighting with (IS)."
Warren did not say whether the ten are fighting in Syria or in Iraq.
In a related context American intelligence official estimated the number of Europeans fighters involved in Syrian opposition about a thousand volunteers, but he did not elaborate on the number of those in the ranks of the Islamic state / IS /, considered by the West most dangerous terror organizations.
The federal American intelligence had arrested several people who were trying to travel from the United States to Syria to join the Islamic State organization.