Olympic swimming gold medallist Klete Keller has been identified as part of the group which stormed the Capitol Building in Washington D.C. last week - wearing United States Olympic apparel.
Supporters of US President Donald Trump halted the Joint Session of Congress, which was being held to certify the election of Joe Biden, on January 6.
The riot resulted in the deaths of five people, with more than 50 people injured.
According to SwimSwam, Keller has been identified in photos and videos from the riot by at least 12 people.
Screenshots show a tall man in a United States Olympic team jacket standing in the rotunda in the Capitol Building.
Keller has now deleted his social media accounts but had previously been a vocal supporter of Trump, who has been accused of inciting the riot.
USA Swimming confirmed to insidethegames that it was aware of the reports.
"We respect private individuals’ and groups’ rights to peacefully protest but in no way condone the actions taken by those at the Capitol last week," the governing body said.
Klete Keller wearing his USA swim jacket and fighting police pic.twitter.com/cccKFnJOff— Cgsg52008 (@cgsg52008) January 12, 2021
The United States Olympic and Paralympic Committee (USOPC) has also condemned the participants of the riot.
"We absolutely condemn the violent actions of the rioters at the US Capitol last week," the USOPC statement said.
"We support the right to peacefully protest and express values and viewpoints in a respectful and lawful manner - that is what makes our democracy strong.
"Sadly, that is not what happened in this case."
There have been calls for both USA Swimming and the USOPC to take action against Keller, who could also face federal charges.
Keller earned two Olympic gold medals and one silver with the American men's 4x200 metres freestyle relay team, triumphing at Athens 2004 and Beijing 2008 and finishing second at Sydney 2000.
The 38-year-old also claimed bronze medals in the men's 400m freestyle at Sydney 2000 and Athens 2004.
There have already been sporting repercussions from the US Capitol riot.
Trump National Golf Club in Bedminster in New Jersey will no longer host the 2022 US Professional Golfers' Association Championship after organisers decided using the course would be "detrimental".
Bill Belichick, coach of National Football League team New England Patriots, also turned down an offer to receive the Presidential Medal of Freedom from Trump.
"Recently, I was offered the opportunity to receive the Presidential Medal of Freedom, which I was flattered by out of respect for what the honour represents and admiration for prior recipients," Belichick said.
"Subsequently, the tragic events of last week occurred and the decision has been made not to move forward with the award."
Newly-elected International Golf Federation President Annika Sörenstam received criticism last week for receiving the Presidential Medal of Freedom from Trump just hours after US Capitol was stormed.