Multiple gunshots were reportedly fired at the US Capitol Thursday, prompting a lockdown of the building and surrounding offices, dpa reported.
The lockdown has since been lifted, the Senate sergeant at arms said.
Local media reported that at least one police officer had been wounded in the incident. Fox News reported that the shootout at the Capitol followed an attempt by a driver to ram a barricade at the White House.
US President Barack Obama had been briefed on the incident.
Details of the incident remained unclear, but Washington police confirmed a shooting investigation near the Capitol, where Congress is currently in the grip of stalled budget talks.