FIFA on Wednesday asked England's Football Association and a newspaper to provide evidence of fresh allegations of corruption at the top of world football, saying they were of "extreme concern".
The move followed widespread media reports in Britain on Wednesday which branded officials "sleazeballs" and "rotten to the core" a day after more claims were made against six decision-makers on FIFA's executive committee.
The secretary general of world football's governing body, Jerome Valcke, sent a letter to the FA asking for a report from former England 2018 chairman Lord David Triesman.
In testimony to a parliamentary hearing in London revealed Tuesday, Triesman named four FIFA executive committee members who had requested cash and a knighthood in exchange for their votes in the 2018 World Cup ballot.
"In his letter to The FA, the FIFA Secretary General expresses the extreme concern of FIFA and the FIFA President (Sepp Blatter) at the latest allegations questioning the integrity of some FIFA Executive Committee members in connection with the bidding procedure for the 2018 and 2022 FIFA World Cups," a FIFA statement said.
Valcke asked for any documentary evidence "to be in a position to examine the situation thoroughly and with clear-sightedness."
He also called on the Sunday Times newspaper to submit any other evidence it had especially on "a whistleblower who had worked with the Qatar bid."
FIFA presidential candidate and Asian football chief Mohamed Bin Hammam on Wednesday denied allegations that Qatar paid bribes to secure the 2022 World Cup.
"I can assure you nothing like this has happened from our side," the Qatari was quoted as saying by Britain's Press Association.
"If someone wants to damage reputations like this then they have to provide the proof. You can't just accuse people just like that," Bin Hammam added.
The same newspaper reported initial bribery allegations last October during the controversial campaign to host the 2018 and 2022 World Cups.
They prompted a FIFA ethics inquiry which led to suspensions for two executive committee members, Reynald Temarii, Oceania's then football chief, and Nigeria's Amos Adamu, for breaches of its ethics code.
The Sunday Times, which provided testimony to the parliamentary commission, had already handed over evidence to Zurich-based global football chiefs at the time including videotaped interviews.
The British Parliament's culture, media and sport committee said Tuesday the newspaper implicated African FIFA officials Issa Hayatou from Cameroon and Jacques Anouma from the Ivory Coast.
In subsequent testimony, Triesman claimed four other FIFA members had been guilty of "improper and unethical" behaviour by requesting favours.
British sports minister Hugh Robertson called for urgent reform of FIFA's World Cup bidding process.
"Leaving FIFA is not on the agenda but all the effort at government level is on trying to get reform at FIFA," Robertson said.
Robertson nonetheless explained that Triesman's allegations would be difficult to prove "because these were just conversations he had with individuals."