Fifa has strongly criticised what it calls a "concerted and ongoing effort" to "undermine" the organisation and its president Gianni Infantino.

The statement follows a Daily Telegraph report, external which claimed Infantino's alleged lover was given a severance payment by Uefa after he had an affair while he was its general secretary.

A Fifa spokesperson told the Telegraph Infantino "strongly denies" the allegations and that they are "categorically untrue".

Fifa has now itself hit out at "unsubstantiated assertions and demonstrably false claims", adding that "speculation and insinuation should not be presented as fact".

Infantino has come under increasing pressure from Uefa and European football associations over his aborted Fifa Forward Enterprise (FFE) proposal.

FFE would have meant a new company being created to manage commercial and ticketing rights, with 21% sold off to a private investment company.

Uefa has said it has lost confidence in Infantino, while Norwegian Football Federation (NFF) president Lise Klaveness on Friday called on the Swiss-Italian to resign.

European football's governing body says its threat to boycott Fifa events remains on the table, adding that assurances the FFE plan could not be revived have not been received.

"The Fifa president was democratically elected by Fifa's Member Associations and continues to serve with their mandate," Fifa said in its statement on Saturday.

"It is increasingly evident that there is a concerted and ongoing effort by some to undermine Fifa and its president.

"Those who do not have the support of Fifa's member associations should not seek to achieve through allegation, insinuation or misinformation what they cannot achieve through Fifa's established democratic processes."

Opposition to Infantino is largely from within Europe.

The Mexican Football Federation broke ranks with its regional governing body Concacaf to come out in support of Infantino.

It echoed a statement from Conmebol - South America's governing body - in saying it would reject any attempt to remove Infantino without a vote involving all 211 Fifa member countries.

Infantino is also unanimously backed by the 54 nations of the Confederation of African Football (Caf).

Scrutiny not licence to distort facts - Fifa

Infantino called members of the Fifa management board to a meeting in Rabat, Morocco on Wednesday.

Fifa issued a statement on behalf of Infantino and secretary general Mattias Grafstrom which apologised for the FFE proposal, but also said it would "no longer tolerate any attacks on its integrity, good governance and due process".

The statement released late on Saturday evening was similarly defensive about the criticism the organisation has faced.

"Change inevitably challenges established interests, but disagreement with that change cannot justify efforts to undermine the democratic mandate of Fifa's president or the institution he was elected to lead," it added.

"Fifa welcomes legitimate scrutiny. But scrutiny is not a licence to distort facts, amplify unsubstantiated allegations or manufacture distractions designed to undermine progress.

"Where reporting is inaccurate or misleading, Fifa will challenge it directly and vigorously."