BETHESDA, Md. - An all-clear has been given following a tense scene at the Walter Reed National Military Medical Center after reports of an active shooter were determined to be a false alarm, according to officials.
Security at Naval Support Activity Bethesda received a call about a report of an active shooter situation in the basement of Building 19 at Walter Reed at around 2 p.m. Tuesday, authorities say.
Following a search, there was no evidence that shots were fired and the all-clear was given about an hour later.
During the incident, Rep. Dutch Ruppersberger (D-Md.) said he was sheltering in place in a conference room at the hospital with about 40 other people.
Army Lt. Col. Audricia Harris, a Pentagon spokeswoman, told Fox News that the supposed active shooter at Walter Reed was only a drill. The U.S. Navy also posted on Twitter that there was no active shooter and it was an "ad hoc drill."
However, there have been conflicting statements by authorities on whether this was a scheduled drill.
"Security responded and cleared the building, finding no indication of an active shooter," Naval Support Activity Bethesda tweeted. "After investigating the call and the origin, NSA Bethesda has determined that this was a false alarm and not part of a scheduled drill as has been reported."
However, the U.S. Navy later posted on Twitter that an error in the use of the mass notification system led to the scare.
"The active shooter event aboard Naval Support Activity Bethesda today was the result of the improper use of a mass notification system by a tenant command aboard the installation. While preparing for an upcoming drill, the notification system was inadvertently enacted without containing the words "EXERCISE" or "DRILL." Individuals who saw the mass notification statement immediately notified NSA Bethesda security, where they responded accordingly and instituted an installation-wide active shooter response. On further investigation, they determined that the improper use of the system was the root cause and secured from the active-shooter response."
Following the all-clear, Ruppersburger said that at no point was there any indication that the incident was a drill.
"People were scared and upset. Drills are important and today was a valuable learning experience for me, but training exercises must be properly communicated," he wrote.
A nurse at Walter Reed, Mary Lock, said she and other employees remained locked down in a second-floor clinic for an hour after hearing this repeated announcement over a loudspeaker: "Active shooter, this is not a drill!"
Lock, 58, said they have had drills for events like this, so she didn't panic.
"It is nerve-wracking as all get out," she said with a laugh as she left work to catch a bus.
The Montgomery County Police Department also responded to the call, sending units after a request for assistance in what seemed like a legitimate report of an active shooter, spokeswoman Lucille Baur said.
"There was no indication from the call that this could be a training exercise," she said.
Walter Reed is the nation's largest military hospital and, according to its website, is among the first stops in the continental United States for troops wounded in combat.
NSAB oversees operational support for its major tenants at the base, including Walter Reed.
Information from the Associated Press used in this report.