The Olympic Council of Ireland has launched an investigation after tickets allocated to the organisation were found on two men arrested for selling fake tickets.

Irish national Kevin Mallon, one of the heads of British ticketing and corporate sports hospitality company, THG Sports, was arrested for conspiracy and helping to sell tickets illegally to the Rio Games, local police said.

The state's investigative police also arrested a company employee who was working as an interpreter during the games in a raid on Friday.

"The OCI has launched an immediate investigation with our (authorised ticket reseller) ATR, Pro10, into how the individuals were allegedly in possession of OCI allocated tickets," the Olympic Council of Ireland said in a statement.