Sepp Blatter has said he will not stand down as Fifa president despite criminal proceedings being opened against him by Swiss investigators.

The Swiss, 79, is suspected of signing a contract that was "unfavourable to Fifa" and making a "disloyal payment" to Uefa president Michel Platini.

Blatter, who will stand down as Fifa president in February, said he had "had done nothing illegal or improper".

Platini, 60, has written a letter to Uefa members denying any wrongdoing.

In a statement released through his lawyers, Blatter said a £1.5m payment made to Platini, the head of European football's governing body, in 2011 was "valid compensation and nothing more".

Both men are also facing investigation by Fifa's independent ethics committee over the payment, which Platini says was for work as Blatter's technical advisor between 1999 and 2002.

World governing body Fifa, which has been hit by a string of corruption allegations in recent years, has said it is co-operating with the investigation.