Keller was appointed earlier this year to investigate dealings between Infantino and Michael Lauber, former Swiss Attorney General.

A statement issued by Keller said he had uncovered "clear signs" that the FIFA President may be "guilty of criminally reprehensible behaviour".

Keller is unable to open an investigation over the use of the private jet, as his brief not does include matters that did not involve Lauber.

"The extraordinary federal prosecutor has completed the examination of the criminal accusations brought against the president of FIFA, Gianni Infantino, for unfair management in connection with the use of a private jet," the statement read.

"There are clear signs that the FIFA president has found guilty of criminally reprehensible behaviour.

"However, these facts fall within the competence of the Public Prosecutor's Office of the Confederation.

"The supervisory authority of the Federal Public Prosecutor's Office (AS-MPC) had tasked Stefan Keller, extraordinary federal prosecutor, to investigate various criminal accusations in meeting Gianni Infantino in connection with the use of a private jet during a trip between Suriname and Switzerland.

"Based on the investigations carried out, Stefan Keller is of the opinion that a criminal investigation must be opened for unfair management."

Keller has sent the findings of his investigation to the Public Prosecutor’s Office.

The office will now "deal with the matter with its own resources".

The case is connected with the use of a private jet to travel between between Suriname and Switzerland.

FIFA has hit back at the statement issued by Keller, which it says is both "malicious and defamatory".

The governing body said it will take "all necessary legal steps" to end the "baseless and ill-intentioned accusations".

"FIFA and the FIFA President are shocked by the statement issued today by 'special prosecutor' Stefan Keller," a FIFA statement to insidethegames read.

"This statement is both malicious and defamatory in nature and demonstrates his extreme bias.

"Now, many months into his investigation and having established precisely nothing problematic about these meetings with the former Federal Attorney General, as FIFA always predicted would be the case, and having not even asked to hear the FIFA President since his investigation was announced last July, the 'special prosecutor' has today issued an official “media release” saying that the FIFA President should now be investigated for something else!

"Neither FIFA nor its President have ever been informed of these new spurious allegations and they are therefore unable to comment on them, which is probably the intention of the 'special prosecutor'.

"The method of 'special prosecutor' Stefan Keller to accuse and defame by publishing media releases without justification borders on character assassination and is rejected in the strongest possible terms by FIFA and its President.

"FIFA and its President will obviously take all necessary legal steps and remedies to put an end to these baseless and ill-intentioned accusations."

The investigatory chamber of FIFA's Ethics Commission both opened and closed an investigation into Infantino’s conduct in August.

Criminal proceedings were opened in July against Infantino in Switzerland over dealings between the FIFA President and Lauber.

The case centres on undocumented meetings that Lauber and Infantino are alleged to have held in 2016 and 2017.

Infantino has insisted his innocence, saying the meetings "were in no way secret and most certainly not illegal".

Infantino became a member of the International Olympic Committee in January.

The Swiss-Italian became FIFA President in 2016 and was re-elected in 2019.