FIFA is investigating allegations of bribery involving presidential candidate Mohamed bin Hammam and FIFA vice president Jack Warner, just days ahead of Sepp Blatter's bid for re-election as head of world soccer's governing body.

The two senior officials will face an ethics investigation at FIFA headquarters on Sunday, three days before bin Hammam challenges Blatter in the presidential election in the June 1 vote by FIFA's 208 national members.

United States official Chuck Blazer, Warner's longtime ally and CONCACAF general secretary, reported the allegations to FIFA.

''In view of the facts alleged in this report, which include bribery allegations, FIFA secretary general Jerome Valcke ... requested the FIFA ethics committee to open ethics proceedings,'' the soccer body said in a statement Wednesday.

The ethics panel can provisionally suspend officials under suspicion while it gathers evidence for a full hearing. It took this path when investigating two of bin Hammam's FIFA executive committee colleagues prior to the 2018 and 2022 World Cup votes last December.

Bin Hammam, under the terms of a provisional ban, could then be prevented from attending any soccer meeting and effectively barred as an election candidate.

FIFA said the bribery allegations related to bin Hammam's meeting with 25 Caribbean soccer leaders on May 10-11 in Warner's native Trinidad to lobby for support.

''This meeting was linked to the upcoming FIFA presidential election,'' FIFA said.

Blatter's campaign adviser, Brian Alexander, said the FIFA president would not comment on the case.

Bin Hammam helped organize the hastily arranged meeting after he was unable to attend the CONCACAF annual congress a week earlier in Miami.

The Qatari official was denied a visa to enter the U.S., despite traveling on a diplomatic passport. His campaign's administrative oversight left Blatter a clear run to lobby for votes in Miami.

Warner has long been a key powerbroker in FIFA politics and his backing was seen as vital to bin Hammam's hopes. Blatter has been endorsed by confederation leaders in Africa, Europe, Oceania and South America.

Warner's 35-member confederation has not yet officially backed either candidate.

Bin Hammam and Warner are both scheduled to be in Zurich on Thursday for a meeting of FIFA's finance committee, and to attend FIFA's executive committee meeting chaired by Blatter on Monday.

They face lengthy suspensions from all soccer duties if bribery allegations are proven. Both were re-elected unopposed this year to lead their continental bodies for four more years.

Two other Caribbean Football Union officials, Debbie Minguell and Jason Sylvester, are being investigated.

FIFA said the four people under suspicion have been invited to ''take a position'' by Friday and report to the ethics panel on Sunday.

Corruption in FIFA has been a prominent campaign theme after a series of financial and vote-buying scandals severely damaged FIFA's reputation during Blatter's 13-year presidency.

Bin Hammam appeared to have been damaged by association with corruption more than Blatter during their two-months of campaigning for votes.

Bin Hammam was a key player in Qatar's successful bid to host the 2022 World Cup. Qatar was accused in a British Parliamentary hearing of paying $1.5 million in bribes to African FIFA executive committee members Issa Hayatou and Jacques Anouma. They deny the claims.

On Wednesday, a whistleblower from the Qatar bid had been scheduled to submit evidence to Valcke and FIFA legal director Marco Villiger in Zurich.

However, FIFA said the whistleblower ''decided not to attend the meeting'' based on legal advice.

As FIFA's top administrator, Valcke must decide whether to refer Qatar's bid to the ethics panel.

Blatter last week neither encouraged, not rejected, speculation that proven corruption connected to the Qatar bid could force FIFA to reopen the 2022 bid contest. It also included the U.S., Australia, Japan and South Korea.

The tiny emirate defeated the U.S. 14-8 in a final round of voting by FIFA's executive committee. Two members, Amos Adamu and Reynald Temarii, were suspended following an ethics probe into vote-buying allegations. Adamu got a three-year ban for seeking bribes and has appealed to the Court of Arbitration for Sport.

Blazer, the highest-ranked American in soccer, was openly critical of the Qatari plans in public, and within FIFA's executive committee that he joined in 1996.

Calls to Blazer were not answered on Wednesday.

Bin Hammam also has been with FIFA for 15 years, while Warner was elected to his seat in 1983.

Warner, along with three more FIFA executive colleagues, also was accused of unethical behavior at British lawmakers' hearing this month.

The former head of England's failed 2018 World Cup bid, David Triesman, said the 68-year-old Trinidad government minister asked for money to build an education center and buy 2010 World Cup broadcast rights for Haiti.

Warner denies the allegation. He was censured by FIFA in 2006 after his family was found to have profited from selling overpriced World Cup ticket packages to Trinidad fans for that year's World Cup in Germany.

FIFA said Warner and bin Hammam would face an ethics panel chaired by Namibian judge Petrus Damaseb.

Ethics committee chairman Claudio Sulser, who passed sentences on Adamu and Temarii, stood aside to avoid a conflict of interest because he shares Swiss nationality with Blatter.