Washington:
Police searched a major US military hospital in a Washington suburb Monday following an unconfirmed report of gunfire at the vast complex.
Staff at the Walter Reed National Medical Center were ordered to shelter in place until police with sniffer dogs had finished inspecting its 20-story main building.
"At this time, there's been no injuries reported (and) no indication, no evidence of any kind ... that there was a shooting," Montgomery County Police spokesman Captain Paul Starks told reporters.
Officers have interviewed the individual who made the initial call at 10:48 am (1448 GMT), he said, without giving further details.
"They heard some noise that they thought could have been shots," he said.
Staff took cover as a "code white" lockdown was declared at the sprawling facility where 7,000 people are employed and security is described as tight.
One member of staff described colleagues and patients hiding in a bathroom with the lights off, amid shouts in the hallways for people to stay put.
Local TV news meanwhile showed hospital staff - some in white smocks - exiting the main building with their hands in the air.
The lockdown at Walter Reed - the nation's premier military hospital - followed a weekend of heightened security in the United States for the Independence Day holiday.
It also came days after a similar unconfirmed report of gunfire prompted a lockdown at the Washington Navy Yard, another major military facility in the US capital.
The Navy Yard was the scene of a mass shooting in September 2013 in which a lone gunman killed 12 people and injured three others.
Walter Reed is regarded as the top US military hospital, with patients ranging from Iraq war veterans to President Barack Obama.