Blatter took the unusual step of issuing an open letter to members of the executive committee on Sunday, telling them a report in Britain's Sunday Times newspaper had created a "very negative impact" on football's governing body.
The report said Nigeria's Amos Adamu had been filmed asking for money for a personal project and that Oceania Football Confederation president Reynald Temarii from Tahiti wanted money for a sports academy.
FIFA is due to announce on December 2 in Zurich which countries will host the two World Cups with the 24-strong executive committee deciding both venues on a majority vote.
"I am sorry to have to inform you of a very unpleasant situation which has developed in relation to an article published today in the Sunday Times, entitled 'World Cup votes for sale'," Blatter wrote at www.fifa.com.
"The information in the article has created a very negative impact on FIFA and on the bidding process for the 2018 and 2022 World Cups."
He added: "I will keep you duly informed of any further developments. In the meantime, I would like to ask you to refrain from making any public comments on this matter."
That request came after Chuck Blazer, the United States representative on the executive committee, told Reuters that the decision on hosts for the next two World Cups was unlikely to be delayed.
"The Ethics Committee will address these issues directly and it should not take them very long to ascertain all the facts," Blazer, speaking in a telephone interview from New York, told Reuters.
"The date of December 2 was chosen specifically ahead of the 'political season' of congresses and elections, and I see no reason why this would be delayed."
The investigation comes after the Sunday Times said its reporters, working undercover, posed as lobbyists for a consortium of American private companies.
VOTING PROCEDURE
Blazer told Reuters: "I cannot comment on these cases individually of course, but what I will say is up to now I have met with five different bidding committees and in some cases visited their countries - England, Russia, Belgium/Holland, Japan and the United States.
"All the bidders I have met have been totally professional in their presentations, not alluding to any other types of benefits and I think that needs to be said.
"They were simply trying to offer the best World Cup proposals.
"I don't think people should get the wrong impression of the FIFA process either. On the contrary, it was not as if journalists have been monitoring a bid that seemed dubious in any way, but they have created a scam, a trap.
"However, it is up to FIFA individuals to be vigilant at all times.
"I do not think there is anything wrong with the voting procedure. We have come to expect it to be carried out morally and ethically based on good judgement and on what has been presented by a bidding committee.
"By having a
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