Reports that U.S. Olympic gold medallist swimmer Ryan Lochte was held up at gunpoint during a party in the early hours of Sunday in Brazil are false, says the International Olympic Committee.

"I can tell you the story is absolutely not true," spokesman Mark Adams said at the Olympic Park, after receiving a message on his mobile phone.

"It's a false story"

"It (the message) is from USOC (United States Olympic Committee). It's a false story."

Fox Sports News had originally reported the incident, and quoted the swimmer's mother as saying the incident had been "terrifying". USOC said it was finding out "truth and details".