The officials describe these as a “handful,” with European countries facing “several dozen” similar cases.
But they believe some were probably recruited by extremists, indoctrinated and provided terror training. And more Americans may be heading over to fight.
The stark assessments have prompted questions from Congress about potential action. So far, the administration hasn't provided answers.
U.S. officials said missile strikes by drone or military aircraft against al-Qaida-linked forces have been considered, even if they are unlikely in the near future.
The Pentagon has advised against any such strikes because of sketchy U.S. intelligence on the rebel forces in Syria, according to two U.S. officials.
To monitor the threat, officials said, the U.S. and its allies are trying to track any Western fighter returning home from Syria.
