WASHINGTON — The U.S. believes there are about a dozen Americans fighting alongside extremist groups in Syria, not more than 100, as has been cited for months.

That’s not to say there is no concern about these other 88 or so Americans who officials say have been killed, arrested, traveled or attempted to travel to join the fight. But the U.S. only knows of about 12 who are in Syria fighting, FBI Director James Comey said.

Comey also said the U.S. believes it knows the identity of the British-accented masked man in the videos depicting the beheadings of two American journalists and a British aid worker. He declined to name the man or reveal his nationality.

He did not address whether the U.S. believes the man actually carried out the killings. The full beheadings are not shown in the videos, but the English-speaking militant holds a long knife and appears to begin cutting the three men, American reporters James Foley and Steven Sotloff and British aid worker David Haines.

The figure of 100 American militants joining the fight in Syria had taken on an urban legend status over the past few months as the Obama administration made its case to the American public for military action in Iraq and Syria. It’s unclear what significance the discrepancy has as far as Americans’ support for the U.S. military action, which so far has been strong.

“When I use a number of more than 100, that means people who have gone and come back, people who have attempted to go and we locked them up, people who have gone and stayed,” Comey said. “The figure that I’ve been operating with is, ballparkish, a dozen still there fighting with terrorist groups.”