The Brazilian authorities have stopped US swimmers Gunnar Bentz and Jack Conger from boarding a flight at Rio de Janeiro airport, the US Olympic Committee has confirmed.
The two men were taken away for questioning about an alleged robbery.
Police have queried their accounts of that robbery they reported in Rio on Sunday.
Two teammates – Ryan Lochte and James Feigen – were barred from leaving the country, but Lochte had already left.
The four swimmers said they had been robbed at gunpoint in a taxi in Rio.
According to reports from the US where Lochte is believed to be at the moment, the robbers stopped the taxi and brandished a police badge before forcing the athletes onto the ground and stealing their money.
But police say their account of when they arrived at the Olympic village does not square with CCTV recordings.