The Department of Defense raised the security level Friday at military bases across the United States in response to growing concern that they could be targeted for attack.
Under Force Protection Condition Bravo — the third of five security levels — more guards may be deployed at base entrances, and people and goods entering bases are likely to be subjected to closer scrutiny.
A spokesman for U.S. Northern Command said it's the first time the security level has been raised nationwide since Sept. 11, 2011, the 10th anniversary of the attacks on New York and Washington.
"There's a lot of different threats that are out there, from ISIS to homegrown violent extremists," spokesman John Cornelio said. "By providing this increase in security measures, we increase the safety and security of our service members.
"It is a fairly significant step. I think it's going to be something that's part of the new normal."
Cornelio said the change was not made in response to a specific threat. But it follows an attack in Texas that officials believe was inspired by the self-declared Islamic State, and a warning from the director of the FBI that thousands of English speakers are taking in the group's propaganda online.
Michael GreenbergerÖ, director of the Center for Health and Homeland Security at the University of Maryland, described the decision as the most visible indication yet of officials' growing concern about the potential for terror attacks at home.
"The whole [Islamic State] threat goes beyond the kinds of things people were worried about with just al-Qaida," he said. "We are in a different stage than we have been since 9/11."
The attention paid to the death of a transgender woman who was shot by guards at the gates of the National Security Agency at Fort Meade is a hint at how much media attention even an abortive attack on a military facility could attract, Greenberger said.
"The thing that is being worried about is more serious than the charging of the NSA gates," he said.
Officials have voiced concerns in recent days about the potential for its rhetoric to inspire so-called lone wolf attacks at home.
Police shot and killed two armed men Sunday in Garland, Texas, outside an event that featured an exhibition of pictures of the Prophet Muhammad.
The event was organized by groups that oppose what they describe as the encroachment of Islam on America. Many Muslims find depictions of the physical image of Muhammad deeply offensive.
After the attack, the Islamic State claimed responsibility for the attack. Officials say they do not think the men were directed to act by terrorists overseas.
On Thursday, FBI director James Comey acknowledged that federal investigators had intelligence suggesting that one of the attackers, Elton SimpsonÖ, planned to attend the event, but not that he planned any violence.
Comey said the Islamic State presented a particular danger because it is proficient at using social media to deliver propaganda. The group has thousands of English-speaking followers online, he said, including many in the United States.
Soon after the Texas attack, a post appeared on an anonymous text-sharing site claiming that the Islamic State has 71 people in 15 states ready to carry out missions. Maryland was one of five states named.
Gov. Larry Hogan's office said Thursday that it did not believe the threat was credible.
While al-Qaida's branch in Yemen has long tried to motivate and direct people in Europe and the United States to commit terror attacks, Greenberger said the Islamic State presents a new, more sophisticated challenge.
Comey said the group's reach through social media is like a siren song for would-be supporters.