The letter, forwarded to the United Nations chief by Iran's ambassador in New York Mohammad Javad Zarif, condemned "American officials for their illegimate and open threats to use force against the Islamic republic of Iran".

"These are in obvious contravention of international rules and the principles of the United Nations," the letter was quoted as saying.

It said that "these rude threats have recently been publicised through some reports in US newspapers", and noted a report in the New Yorker magazine that US planners had even looked into using nuclear 'bunker-busters' to strike Iran's atomic facilities.

"These (threats) have entered a new stage, with the refusal of US officials to deny these reports," the letter said.

"Therefore it is necessary for the United Nations and the Security Council to pay serious attention to these threats and illegal remarks and take quick and firm action," the letter said.