The U.S. military has increased security at bases across the country, after the FBI expressed concern that Islamist militants could target troops or police officers.

The U.S. Northern Command said the move was due to “recent events” but stressed that the “change is not tied to a specific, credible threat.”  The command also said it shares FBI concerns about “potential threat posed by homegrown violent extremists.”

On Thursday, FBI Director James Comey said there might be thousands of Islamic State (IS) followers online in the U.S.

“Hundreds, maybe thousan

ds of people across the country who are receiving recruitment overtures from the terrorist group or directives to attack the United States,” Comey said. “We have a general concern, obviously, that ISIL is focusing on the uniformed military and law enforcement,” he added, using another common acronym for the Islamic State.

Last Sunday, two gunmen attacked an event in Garland, Texas, where cartoons lampooning Islam’s Prophet Muhammad were being judged in a “contest.”

The IS group claimed responsibility for the incident, but U.S. officials said there was insufficient evidence to decide whether the group actually carried out the attack.

“This is still under investigation by the FBI and other members of the intelligence community to determine any ties or affiliations that these two individuals may have had with ISIL or other terrorist organizations around the world,” White House spokesman Josh Earnest said.

Police have identified the assailants in the attack as Elton Simpson and Nadir Soofi, who shared an apartment in the neighboring Phoenix, Arizona. The pair opened fire at a conference center, wounding a security guard, before they were shot and killed by Garland police officers.

VOA’s Jeff Seldin contributed to this report from the Pentagon.

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