The head of the Olympic Council of Ireland (OCI) has stepped aside from his role after being arrested in Brazil as part of an investigation into the alleged illegal sale of tickets for Rio 2016.
Patrick Hickey, who has been treated for chest pain at a hospital in Rio, has also stepped aside from his positions as the International Olympic Committee member in Ireland, president of the European Olympic Committees and vice president of the Association of National Olympic Committees.
The organisation said: "In light of this morning's developments and his ill health, Mr Hickey has taken the decision to step aside temporarily as president of the OCI and all other Olympic functions (IOC member in Ireland, EOC president, ANOC vice president) until this matter is fully resolved.
"Mr Hickey will of course continue to co-operate and assist with all ongoing inquiries."
Mark Adams, director of communications for the International Olympic Committee, said the organisation would co-operate fully with police.
"What I can tell you is that it involves 1,000 tickets of the six million tickets (for the games)," he said.
"We have full confidence in the system here and we believe here, as with everywhere, that everyone is innocent until any guilt can be proved or, in fact, any charges have been brought."
Ireland's Sports Minister Shane Ross cut short his trip to the Games to hold crisis talks over the affair in Dublin with Attorney General Maire Whelan, colleagues and officials.
Mr Ross said: "Given the seriousness of this matter, and in the interests of taking swift and decisive action, I will be returning to Dublin as quickly as possible."
Mr Hickey is being supported by Irish diplomats in Brazil.
The authorised ticket reseller (ATR) contracted by the OCI is Dublin-based PRO10 Sports Management. The company said it has always acted properly and fully within the guidelines.
"The allegation that a portion of the OCI's family and friends tickets were being made available for general sale is utterly untrue and completely without any foundation," the company said.
Mr Hickey had previously denied any wrongdoing.