UPDATE:  (AP) - The U.S. Capitol building is no longer on lockdown.

The Senate sergeant at arms said a lockdown had concluded. The sergeant at arms had earlier issued a lockdown alert for the building and visitor center, saying police activity has been reported.

Capitol police had said they were searching for an individual but offered no details. One officer outside the Capitol said police are responding to sketchy reports of woman who may have a gun; a House Democratic leadership staffer had said the sergeant at arms office had said there had been a woman with a gun in a tunnel leading to the Rayburn House Office Building.

PREVIOUS STORY: The U.S. Capitol building is on lockdown Friday morning out of an abundance of caution due to police activity.

Everyone is being asked to shelter in place.

Those inside have been told to close, lock and stay away from external doors and windows, and to silence mobile phones. No one is permitted to enter or exit until directed by U.S. Capitol Police.