FIFA has asked German magazine Der Spiegel to hand over all the documents it says it has regarding the claims of convicted match-fixer Wilson Raj Perumal that Cameroon players threw their World Cup group games.
FIFA has refused to make any comment regarding the allegations that some Cameroon players fixed the results of their three Group A matches, which all ended in defeat, nor would it confirm or deny it was investigating the claims.
Ralf Mutschke, FIFA's head of security, cast doubt on Perumal's claims and said the ruling body wanted to see what proof Der Spiegel had.
"FIFA has substantial doubts about the allegations published by Der Spiegel," he said in a statement.
"As such FIFA has asked Der Spiegel to provide us with all the communications with Perumal and any other material they claim to possess in order to prove the allegations they have made in public.
"This article has put the integrity of the FIFA World Cup matches in question, which is a serious allegation.
"We have carefully monitored all 56 games to date and we will continue to monitor the remaining eight matches. So far we have found no indication of any manipulation on the betting market of any World Cup matches."
"I did not predict the result of the Cameroon vs Croatia match" - Wilson Raj Perumal
FIFA president Sepp Blatter said in Rio de Janeiro: "Yes, I have been told about this, but let them do their work on this investigation."
The Cameroon FA said on Monday that it was to investigate claims of match-fixing by their players, especially the game against Croatia, which they lost 4-0.
Perumal, a convicted match-fixer, has subsequently denied Der Spiegel's claims that he predicted the result of the match before it took place or that a Cameroon player would be sent-off before half-time, which is what happened.
In a statement issued on his behalf by the company publishing his memoirs, Perumal said he made his comments three days after the match and not before it took place.
The International Centre for Sport Security (ICSS), which works closely with FIFA and police on match-fixing and related security issues, said yesterday there were no suspicious betting patterns.
"The advice we have received from the legal or so-called 'regulated' sport betting industry is that there was no observable suspicious betting on this match," the ICSS said.