The US Capitol was locked down on Saturday after shots were fired nearby, but police have "neutralized" the suspected shooter, US Capitol police said.
Police were also investigating a suspicious package close to the complex in Washington.
"The Capitol has been locked down because of the potential security threat. No one can enter or exit," Capitol Police spokeswoman Kimberly Schneider said in a statement.
Police did not give details of what happened to the suspected shooter.
However, several media reports including NBC and the Associated Press said the man had committed suicide, and that he left behind a suitcase that was being investigating by a bomb squad.
The incident, which is not believed to be an act of terrorism, occurred on a Saturday and Congress is out of session.
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The number of people missing from last week's Washington state mudslide is revised down from 90 to 22, as the death toll increases to 24, US officials say.
The official death toll in the Washington mudslide has risen to 21, emergency service officials tell Reuters.
The number of people killed after a devastating mudslide in Washington State has risen to 18, authorities confirmed.
The tally of those missing after a large mudslide in Washington State has dropped to 30 from 90, authorities have said.
The body of one more person killed in a Washington state mudslide was found in the debris field where searchers are scouring the muck for about 90 people missing nearly a week after the disaster, a county official said.
Snohomish County Executive Director Gary Haakenson said that person was not included in the official death toll of 17, which remained steady.
The new remains appeared to bring to 10 the number of victims that authorities have said have been found but not yet identified or added to the official death toll.
The Snohomish County government tweeted:
Washington state authorities have warned the number of people killed in the recent mudslide will go up substantially within the next two days.
Sixteen bodies have been recovered, but officials say at least nine more had been found and they expect that number to rise in the next 24 to 48 hours.
Snohomish County District 21 fire chief Travis Hots said that officials are not going to count additional recovered victims until the medical examiner's office has caught up with the recovery effort.
There are 90 people confirmed missing, with another 35 who authorities are unsure were in the area when a hillside collapsed Saturday morning 55 miles northeast of Seattle.
Washington state officials said the death toll following a devastating mudslide remains at 24 and the number presumed missing has been reduced from 176 to 90.