The United Nations Palestine expert has been condemned by UN General-Secretary Ban Ki Moon for suggesting that the US government was behind the September 11 terror attacks.

Writing on his blog in the wake of the Arizona shootings, Richard Falk said: “Let us remember that what seems most disturbing about the 9/11 controversy is the widespread aversion by government and media to the evidence that suggests, at the very least, the need for an independent investigation that proceeds with no holds barred.”

He has expressed similar views on a number of occasions, including in a book on the attacks by renowned conspiracy-theorist Ray Griffin. In 2008 Mr Falk compared Israeli policies towards the Palestinians to those of the Nazis against the Jews.

Mr Ban described the comments about the September 11 attacks as “preposterous”.

His spokesman Vijay Nambiar wrote to Hillel Neuer, executive director of the organisation UN Watch , expressing the view that somebody of Mr Falk’s position had “a clear responsibility to uphold the high standards of the United Nations and the Council”.

He said: “The Secretary-General condemns [Mr Falk’s] remarks. He has repeatedly stated his view that any such suggestion is…an affront to the memory of the more than 3,000 people who died in the attack.”

Mr Neuer said: "We welcome the Secretary-General's unequivocal condemnation of the despicable comments by this official of the UN Human Rights Council.”

However he called on Mr Ban and UN rights chief Navi Pillay “to take the next logical step and call on Falk - who is a serial offender with zero credibility - to be removed.”

The Secretary-General said that it was for the Human Rights Council to decide whether Mr Falk keeps his position. His term is set to expire in May but would likely be eligible for automatic renewal.