US Olympic swimmers Gunnar Bentz and Jack Conger walk to the airport police station office at Rio's international airport in this still frame taken from video dated August 17, 2016, in Rio De Janeiro, Brazil. [Photo/Agencies]

RIO DE JANEIRO - Four US Olympic swimmers have been accused of vandalizing a gasoline station as further doubts emerged about their supposed robbery in Rio de Janeiro.

The owner of the gas station in the Barra da Tijuca neighborhood said Ryan Lochte, James Feigen, Gunnar Bentz and Jack Conger urinated on the premises despite being asked to use the toilet.

"They went to the side of the station and urinated all over [the wall]," the owner, who asked not to be named, was quoted as saying by the Globo newspaper on Thursday.

"We even have images of one of their backsides. They didn't obey the request [to use the toilet]."

The owner added that one of the athletes then damaged an advertising sign.

"It was pure vandalism", he said.

The swimmers claimed they were robbed at gunpoint after their taxi was stopped by thieves posing as police on Sunday morning.

The athletes said they were returning to the Olympic Village after celebrating the end of the swimming competition at the Rio Olympics.

On Wednesday a Brazilian judge barred the swimmers from leaving the country, citing conflicting versions of the incident.

Lochte had already returned to the US but Bentz and Conger were stopped by federal police from boarding a plane at Rio's international airport on Wednesday night. Feigen was said to still be in Brazil.

Lochte, 32, has won six Olympic gold medals, including his victory with the USA's 4x200m freestyle relay team in Rio.