Two US Olympic swimmers flew home from Brazil on Thursday after a local crowd jeered them, calling them "liars" and "fakes", and police accused them of fabricating a story about being robbed at gunpoint during the Rio Games.

Their departure marked what the US Olympic team hopes will be the closing stages of an incident that has embarrassed the host city, angered the police and government, unleashed a storm on social media and dominated news coverage of South America’s first Olympics.

The US Olympic Committee issued an apology after the departure of Gunnar Bentz and Jack Conger, who were among four US swimmers whose account of being stopped by gunmen posing as police early Sunday was disproved.

"We apologize to our hosts in Rio and the people of Brazil for this distracting ordeal in the midst of what should rightly be a celebration of excellence," USOC head Scott Blackmun said in a statement.

The statement confirmed police allegations, including that one of the swimmers had vandalized the gas station after the group stopped there to use the restroom during a taxi ride back to Olympic Village after a late-night party in the city.

After days of standing by the swimmers’ story, the USOC backed up other police evidence, including a security video showing the swimmers in an argument with staff at the Shell service station.

"An argument ensued between the athletes and two armed gas station security staff, who displayed their weapons ... and demanded the athletes provide a monetary payment," it said, adding that the guards allowed the swimmers to leave once some cash had been handed over.

Apart from Bentz and Conger, the incident involved gold medalists Ryan Lochte and Jimmy Feigen.

"The behavior of these athletes is not acceptable," the USOC said, adding that it would further review the incident.