LONDON (Reuters) - U.S. authorities are pursuing hundreds of active counter-terrorism investigations embracing all 50 American states, a senior U.S. Justice Department official said on Wednesday.
John Carlin, Assistant U.S. Attorney General in charge of the department's National Security Division, speaking to journalists in London, said in the last two weeks alone, federal authorities had made 10 counter-terrorism related arrests.
A second U.S. official indicated that investigators believed some of these cases involved potentially active attack plots, though he provided no details.
The Islamic State "wants individuals to conduct an attack in the United States and they are doing everything they can to try to advance that goal," said Carlin, whose visit to Britain included consultations with British security officials.
Over the last six months, Carlin said, U.S. investigators had noticed a change in tactics by the Syria-based Islamic State group. The group had become particularly adept at using social media to pitch sophisticated recruitment messages towards an increasingly young target audience.
Sixty percent of the Islamic State's target audience, by the official's estimate, is aged 25 or younger and a substantial subset of that group are under 21, including many juveniles.
Carlin said American government agencies estimate about 180 Americans had traveled abroad possibly to join militant groups in the Middle East and Africa, though some may have gone to serve as relief workers or fight with moderate forces, such as Kurds or more secular Syrian rebels, against Jihadist militants.
The proportion of Americans traveling to join such groups, compared to the overall US population, is much smaller than similar statistics for European countries, he said. European security officials estimate 700 would be fighters have traveled from Britain alone to militant groups in the Middle East and Africa, and up to half have already returned.