WASHINGTON - The US Senate was locked down on Wednesday afternoon as US Capitol Police investigated reports of "an active shooter" in the office buildings.

"Our officers are searching in and around the Senate office buildings in response to a concerning 911 call. Please stay away from the area as we are still investigating," US Capitol Police tweeted at 2:45 pm (1845 GMT).

US Capitol Police asked people inside the Senate buildings to shelter in place as police officers were searching the buildings for the suspected shooter. An all-clear was given at 4:04 pm (2004 GMT). US Capitol Police said later it was standing by to prepare the Senate office buildings for re-opening.

US Capitol Police Chief Thomas Manger told reporters that the 911 call about an active shooter might have been a bogus one and that there was no confirmation of an active shooter.

The Senate is currently in summer recess and most lawmakers are not in Washington, DC.