The US’s main government building was put on lockdown after reports that a gunman was inside.
Police barred people from entering the US Capitol building, while the Senate sergeant at arms issued a lockdown alert for the building and visitor centre.
Capitol police said they were searching for an armed female congressional staffer, but have provided no further details.
The lockdown was lifted 40 minutes after being enforced, but it is not clear if officials found the armed employee.
One lawmaker told The Hill that a firearm had made it past security, despite there being metal detectors and police officers conducting routine screening of anyone entering the Capitol.
Those working in the building were told to go into an office room and ‘close, lock and stay away from external doors and windows’.
Officials said the chamber met briefly, but recessed ‘immediately’.
The closure came just hours after the killing of five police officers in Dallas, Texas, this morning.