Sepp Blatter says it was "not acceptable" to be accused at a public event of likely knowing senior FIFA officials were corrupt but staying silent.

The former FIFA president was visibly angry, later telling reporters at the University of Basel: "I am not guilty."

Blatter was the key speaker in a debate on problems facing world soccer's governing body, which closed with the claim made by Luis Moreno Ocampo, a former candidate to be FIFA's ethics prosecutor.

Ocampo suggested "the real problem with Mr. Blatter" was knowing about bribery in North and South American soccer which U.S. federal prosecutors revealed last year.

The Argentine lawyer told the mostly student audience that "probably (Blatter) knew and he decided to stay in silence."

Blatter says he was "very unhappy" with Ocampo's accusation.