Police in Brazil have reportedly cast doubt over Ryan Lochte's claims that he and his fellow US swimmers were robbed in Rio de Janeiro.

The authorities have ordered for Lochte and Jimmy Feigen's passports to be seized to prevent them from leaving the country, but the former is already back in the United States, according to his attorney Jeff Ostrow.

According to TMZ, Brazilian judges sent out "search warrants" after the police found 'little evidence' that the alleged robbery took place.

Lochte - a 12-time Olympic medallist - revealed earlier this week that he, Feigen, Gunnar Bentz and Jack Conger were returning to the Athletes' Village on Sunday when they were stopped by thieves posing as police.

After news that the Brazilian authorities wanted to question Lochte and his teammates further, Ostrow told US website TMZ: "I have no information from Brazilian authorities that they want his passport.

"I'm shocked to hear that they would go to such measures in an effort to further investigate the incident as he has been nothing but cooperative with authorities, including sitting for a full interview with the Tourist Police, US State Department, USOC Security, FBI, and anyone else that requested to be present."

None of the swimmers were hurt during the incident.