The report of Walter Reed's "active shooter" was actually an exercise, says the Pentagon

Reports of an active shooter at the Walter Reed Military Hospital in Bethesda, Maryland on Tuesday, have been confirmed to be an exercise, officials said.

Lieutenant-Colonel of the Army, Audricia Harris, a Pentagon spokesman, told Fox News that there was no active shooter at the medical center.

"We are all clear, Secure Code White," tweeted the hospital staff after it was confirmed that there had been no active fire.

Earlier Tuesday, Dutch representative Ruppersberger, D-Md., tweeted that he was "safe in a conference room with about 40 other people" in the hospital, "where we were told that there was an active shooter".

The congressman, whose Twitter account indicated at one point that he "did not believe it's an exercise," tweeted after all clearly that "to no time, nothing indicated that it was an exercise. "

The medical center confirmed that the building was locked out and that an alert had been sent concerning an active shooter. Bethesda Naval Support Activity tweeted this security "cleared the basement of building 19", which, according to officials, was locked.

"No indication to date of an active shooter," wrote NSA Bethesda.

Montgomery County Police tweeted that they were called to Walter Reed at 2:23 pm "to help with the report of a possible active shooter." The US Navy also tweeted that officials were aware of the information and that they had not confirmed the presence of an active shooter at the medical center.

Tuesday's incident follows a series of repeated false alerts from active shooters at many US military bases across the country.

Lucas Tomlinson, Jennifer Griffin and Jake Gibson of Fox News contributed to this report.