Iran has strongly criticised the US at the United Nations, accusing Washington of threatening to launch a military strike against its nuclear facilities.
In a letter delivered to Secretary General Kofi Annan, Iran said the US was "openly" planning to attack Iran in breach of international law.
Officials from the five permanent members of the UN Security Council will discuss Iran in Paris on Tuesday.
Iran has resisted calls by the UN for it to suspend uranium enrichment.
The rhetoric between the US and Iran has become more heated following the UN nuclear watchdog's report on Friday which found Tehran had not complied with a UN demand to end uranium enrichment, says the BBC's Laura Trevelyan at the UN.
Tehran insists it has the right to a peaceful nuclear energy programme, although the US suspects it is trying to develop atomic weapons.
'Illegitimate'
In the letter to Mr Annan, Iran's ambassador to the UN criticised US President George W Bush, who has refused to rule out even a nuclear strike on Iranian targets.
US rhetoric amounted to "illegitimate and open threats to use force against the Islamic Republic of Iran," the letter said.
"These are in obvious contravention of international rules and the principles of the United Nations."
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