Zurich - FIFA announced they have opened an investigation into president Sepp Blatter on Friday as the corruption scandal gripping world football took another extraordinary twist.
A statement from football's governing body said Blatter had been ordered to appear before FIFA's ethics committee on Sunday to respond to claims that he knew about alleged cash payments to Caribbean officials.
The ethics proceedings against Blatter follows a request by Asian Football Confederation (AFC) president Mohamed Bin-Hammam, who is attempting to unseat the FIFA chief at elections in Zurich on June 1.
Friday's announcement came just two days after Bin Hammam, FIFA vice-president Jack Warner and two Caribbean Football Union officials were summoned to the ethics committee to answer corruption allegations.
Bin Hammam and Warner were targeted after Chuck Blazer, general secretary of regional footballing body CONCACAF, reported possible misdeeds during a May 10 and 11 meeting in Trinidad.
The meeting was organised as part of bin Hammam's campaign to drum up support for his presidential bid.
Bin Hammam has strongly denied the allegations and on Thursday called for Blatter to be questioned by the ethics committee, saying the FIFA boss "was informed of, but did not oppose" payments made to Caribbean officials.
FIFA's statement on Friday said Blatter had been summoned to appear before the ethics committee to answer claims that Warner had told him in advance of alleged payments made at the meeting.
The statement continued: "Subsequently, the FIFA Ethics Committee today opened a procedure against the FIFA President in compliance with art. 16 of the FIFA Code of Ethics.
"Joseph S. Blatter has been invited to take position by May 28, 2011, 11:00 CET and to attend a hearing by the FIFA Ethics Committee at the Home of FIFA (Zurich) on 29 May 2011."