More than 200 Americans have traveled or attempted to travel to Syria to fight for Islamic militants, Federal Bureau of Investigation chief James Comey said on Wednesday.
"We continue to identify individuals who seek to join the ranks of foreign fighters ... and also homegrown violent extremists who may aspire to attack the United States from within," Comey told lawmakers on the Senate Select Committee on Intelligence.
People accused of trying to join ISIS/recruited by ISIS
Over 200 Americans have gone or tried to go to Syria to fight: FBI
ANKARA, TURKEY - MARCH 17: A passport photo alleged to belong to 22-years-old British woman Jalila Henry and to have been used by her twin sister Jamila Henry (known and named by Turkish officials as Jaila Nadra H) as she tried to travel through Turkey to Syria to join Daesh (Islamic State of Iraq and Levant) terrorists. Jaila Nadra H was detained after an operation staged by the Turkey's Ankara Province Police Anti-terrorism department in the city's bus terminal in Ankara, Turkey on March 17, 2015. (Photo by Turkish National Police/Anadolu Agency/Getty Images)
Renu Begum, eldest sister of Shamima Begum, 15, holds her sister's photo as she is interviewed by the media at New Scotland Yard, as the relatives of three missing schoolgirls believed to have fled to Syria to join Islamic State have pleaded for them to return home, on February 22, 2015 in London, England. Police are urgently trying to trace Shamima Begum, 15, Kadiza Sultana, 16, and 15-year-old Amira Abase after they flew to Istanbul in Turkey from Gatwick Airport on Tuesday. (Photo by Laura Lean - WPA Pool/Getty Images)
ANKARA, TURKEY - MARCH 17: A 22-years-old British woman, Jamila Henry (known and named by Turkish officials as Jaila Nadra H) who is alleged to have tried to travel through Turkey to Syria to join Daesh (Islamic State of Iraq and Levant) terrorists, who has been detained after an operation staged by the Turkey's Ankara Province Police Anti-terrorism department in the city's bus terminal in Ankara, Turkey on March 17, 2015. (Photo by Turkish National Police/Anadolu Agency/Getty Images)
Handout still taken from CCTV issued by the Metropolitan Police of (left to right) 15-year-old Amira Abase, Kadiza Sultana,16 and Shamima Begum,15 at Gatwick airport, before they caught their flight to Turkey. Metropolitan Police officers are in Turkey as the search continues for three missing schoolgirls believed to have fled to Syria to join Islamic State.
Fighters from the Iraqi Imam Ali Brigade, take part in a training exercise in Iraq's central city of Najaf on March 7, 2015, ahead of joining the military operation in the city of Tikrit. Some 30,000 Iraqi security forces members and allied fighters launched an operation to retake Tikrit at the beginning of March, the largest of its kind since Islamic State (IS) group forces overran swathes of territory last June. AFP PHOTO / HAIDAR HAMDANI (Photo credit should read HAIDAR HAMDANI/AFP/Getty Images)
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The radicalization of Americans by Islamic State is a top concern for the agency, and earlier on Wednesday Comey urged technology companies to allow law enforcement authorities access to encrypted communications to help combat the threat.