The Olympic gold medal-winning swimmer Ryan Lochte has reportedly been held up at gunpoint returning from a party in Rio.

Mr Lochte is now thought to be safe and unhurt at the Team USA base.

He is reported to have contacted his mother Ileana after the incident, and she is said to have described the incident as “terrifying”.

The gunpoint incident reportedly occurred after Mr Lochte, 32, who won gold in Wednesday's 4x200 freestyle relay, and three of his American teammates were invited to a party by the Brazilian swimmer Thiago Pereira.

The incident, first reported by Fox News, was denied by the International Olympic Committee, whose spokesman Mark Adams told reporters in Rio: "The story is absolutely not true."

But Ileana Lochte repeated her claims of a hold-up to the American newspaper USA Today, saying that her son was with at least one US teammate in a taxi when the cab stopped to get petrol. She said the group was confronted by people armed with guns and knives.

“They just took their wallets and basically that was it,” Ms Lochte told USA Today. “I think they’re all shaken up.”

She added that her son told her about the hold-up by text message soon after it happened. Ms Lochte, who is in Rio, said she was on her way to see her son. “I’ll be OK when I see him,” she said.

Ms Lochte's account, however, also seemed to be at least partially disputed by the swimmer’s personal coach, who texted USA Today that Mr Lochte “was not held up”. David Marsh added that he was trying to establish exactly what had happened.

Rio 2016: How the Olympic Games have fared one week on

If confirmed, the incident involving Mr Lochte will be the most high profile of a series of security incidents that have caused problems at an Olympics already overshadowed by the Zika virus and swimming pool water that mysteriously turned green.

In June, before the games even began, the Australian wheelchair basketball player Liesl Tesch warned that Rio was a “dangerous place” after two armed thieves demanded money and stole her bicycle as she trained in the city. The Australian team then had a laptop and Zika-protective team shirts stolen from their quarters in the Olympic village, after about 100 team members had been evacuated because of a small fire in the basement car park of their accommodation.

Evgeny Korotyshkin, a Russian former Olympic swimmer, visiting Rio as president of the Moscow swimming association, also claimed to have been robbed by gun-toting teenagers who let him photograph them in exchange for all the money he had on him.

Among non-athletes, a bus carrying journalists from the basketball venue to the main Olympic park was attacked on 9 August. Witnesses reported what sounded like gunshots hitting the vehicle, shattering windows and leaving two people with minor cuts from flying glass.

Mr Lochte's victory in the men’s 4x200 freestyle relay on Wednesday brought his career Olympic medal tally to 12, making him the second most decorated male Olympic swimmer ever, behind only his teammate and fellow relay winner Michael Phelps. He tweeted a series of pictures of him and his teammates posing with their medals, calling it "an amazing night" and saying: "Four Olympics straight we've won this relay.So humbled to be part of this movement."

Lochte won his first Olympic gold medal in the 4x200 men’s freestyle relay in Athens in 2004. He also won a silver medal at the Athens games after coming second in the individual 200m relay. He won gold with a world record time in the 200m backstroke at the 2008 Beijing Olympics, where he also picked up another relay gold.