WASHINGTON • A recruiting push by Islamic State in Iraq and Syria (ISIS) militants via thousands of Twitter accounts and other social media postings remains one of the biggest threats facing the United States, according to a high-level American military official.
Admiral Bill Gortney, commander of US Northern Command and the North American Aerospace Defence Command, said he was particularly concerned about radicalised US youth "in receive mode", but not communicating back.
The US authorities could potentially track recruits who communicate with ISIS recruiters, but it was tougher to identify potential recruits, such as the shooter who killed five servicemen in Tennessee in July, Adm Gortney said at an event on Wednesday hosted by the Atlantic Council think-tank.
He said heightened security at military bases around the US - now at the highest level in nearly four years - would likely remain in effect for "quite some time", given the government's inability to predict when or where such attacks could occur.
"It is going to be a long slog," Adm Gortney said, adding that the US needed to counter ISIS' narrative. "It is a war of words... We have to go after and break this pattern of radicalisation."
He said the government was doing a comprehensive review of its efforts to counter ISIS' recruitment drive, but the fight had to be led at the local level by parents, communities and schools, not the military.
Adm Gortney ordered increased security in May, affecting everything from recruiting stations to National Guard posts and military bases and camps in continental US, Alaska and US territory in the Caribbean. The move came after two men opened fire outside an exhibit of caricatures of Prophet Muhammad in Garland, Texas; they were shot dead by police.
The two were later found to have had contact with militants, including a British man linked to Syria- based ISIS rebels.
Investigators believe the Garland attackers and the Tennessee shooter principally radicalised themselves through Internet contacts, and were not directly ordered or encouraged to carry out the attack by ISIS leaders.
Adm Gortney said his staff members were working with the intelligence community to find out when the threat level could be lowered, but warned it would be slow.
The admiral also touched on North Korea, telling his audience that Washington believes Pyongyang had the capability to launch a nuclear weapon against the US homeland.
He said it was very difficult to predict the behaviour of North Korean leader Kim Jong Un, but that the US military was prepared to respond if he were to use a nuclear weapon.