RIO DE JANEIRO (Reuters) - Brazilian police said on Wednesday Olympic gold medallist swimmer Ryan Lochte had returned to the United States before a judge's order to stop him but they were searching for his team-mate amid doubts over their account of being robbed at gunpoint in Rio.

Judge Keyla Blanc, of Brazil's Special Tribunal for Fans and Major Events, ordered police on Wednesday to seize the passports of Lochte and fellow gold medallist James Feigen so they could be questioned over inconsistencies in their descriptions of the robbery at the weekend.

Police discovered after checks at Rio's international airport that Lochte, 32, had already left Brazil, where he won a relay gold medal in the Olympic swimming competition that ended on Saturday.

Lochte left for the United States on Monday aboard a commercial flight before the judge's order was issued, a spokesman for federal police said. Feigen was still in Rio de Janeiro, the spokesman said.

The San Antonio Express-News quoted Feigen as saying by telephone that he was in Brazil but declining further comment.

People magazine reported that Lochte, one of swimming's most decorated Olympians, was spotted at an airport in North Carolina on Wednesday with his girlfriend Kayla Rae Reid, a Playboy model. It was not immediately possible to confirm this.

Lochte's attorney did not return calls for comment.

A U.S. Olympic Committee (Usoc) spokesman said police had arrived at the Athletes' Village on Wednesday and asked to meet the swimmers and collect their passports.

"The swim team moved out of the village after their competition ended, so we were not able to make the athletes available," said Usoc spokesman Patrick Sandusky, who could not confirm the swimmers' location for security reasons. "We will continue to cooperate with Brazilian authorities."

A spokesman for the U.S. consulate in Rio declined to answer specific questions on the case but said parties should work with Brazilian law enforcement in the investigation.

Judicial sources said the judge would consider whether to ask Lochte to return to Brazil to give testimony or allow him to do so in the United States.

On Sunday, Lochte told U.S. media that he, Feigen and two other team-mates were travelling to the Athletes' Village in a taxi in the early hours of the morning, after a party hosted by the French Olympic delegation, when armed men carrying police badges pulled them over.

The gunmen ordered them to drop to the ground and demanded their wallets and belongings, Lochte said, adding that he had initially tried to resist.

"The guy pulled out his gun, he cocked it, put it to my forehead and he said, 'Get down,' and I put my hands up, I was like 'whatever'," he told NBC. "He took our money, he took my wallet - he left my cell phone, he left my credentials."

He said the swimmers had US$400 (S$536) stolen. Police sources have told Reuters in recent days they have been unable to find the taxi driver or to corroborate any testimony provided by the swimmers.

On Wednesday, police issued an appeal for the taxi driver to come forward.

The judicial sources said the judge in her ruling pointed to an inconsistency between Lochte, who had said only one man was involved in the robbery, and his team-mate, who testified that several men had robbed them.

The judge also noted that video footage of the swimmers showed them returning to the Athletes Village physically well and joking with one another, and in possession of many of their belongings, including cellular phones and Olympic accreditation.

She also noted that some of the swimmers said they left a party at the French Olympic delegation just after 4am but security cameras showed them arriving at the Athletes Village at around 7am - a journey that would normally only take around 30 minutes at that hour of day.

O Globo newspaper reported that authorities had requested a search warrant for the swimmers' accommodation, with the aim of finding Feigen's cellphone in order to identify exactly where the swimmers were on Sunday night.

On his official Twitter account, Lochte said: "My hair is going back to its normal colour tomorrow", in what appeared to be a tongue-in-cheek reference to changing his appearance.

The swimmer competed in Rio with his hair dyed peroxide blond.