Walter Reed swept for bomb amid scare

Updated 1:58 PM ET

(CBS/AP) WASHINGTON - A bomb threat has been called in to the Walter Reed National Military Medical Center, forcing a building to be closed for three hours at the facility outside Washington.

A military official says someone phoned in a threat minutes before 9 a.m. EDT Wednesday, saying a bomb would detonate about an hour later in the center's America building, which contains a group of clinics.

The official spoke on condition of anonymity because he was not authorized to publicly release information about the incident. He says the building was swept for explosives, and none was found.

According to CBS News, the Navy had said that a sweep for a bomb at Walter Reed National Military Medical Center in Bethesda, Maryland was almost complete following earlier reports of a possible threat.

CBS affiliate WUSA in Washington, D.C. obtained an email that was sent to the Walter Reed staff that read in part:

"Code BLACK"

"In response to a security concern we are currently in a Code BLACK level of security. As a result, building 19 (American Building) no personnel, patients or visitors are allowed in this building and no one is allowed to leave.

"Code BLACK will remain in effect until further notice and additional information will be shared with WRNMMC personnel through their Chain of Command and WRNMMC postmasters."

Earlier, the center announced on its website that "all appointments at Walter Reed Bethesda" have been suspended until 13:00." On its Facebook page, the center published a post around 1 p.m. that appointments have resumed.