The United States will be held legally responsible in the event of an Israeli attack on Iran's nuclear facilities. This was warned by the Foreign Minister of the Islamic Republic, Abbas Araqchi, quoted by "Reuters".
He made his comment after information emerged that Israel may be preparing strikes against Iran.
Iran and the United States - Israel's closest ally - will hold a fifth round of nuclear talks in Rome tomorrow amid deep disagreements over Iran's uranium enrichment, which Washington says could lead to the development of nuclear bombs. Iran denies any such intention.
On Tuesday, CNN reported that it was unclear whether Israel had made a final decision on military action and that US officials were divided on whether the Israelis would ultimately decide to attack.
"Iran strongly warns against any adventurism by the Zionist regime of Israel and will respond decisively to any threat or illegal action by that regime," Araqchi stressed in a letter addressed to UN Secretary-General Antonio Guterres.
He indicated that Iran would view Washington as a "participant" in any such attack, and Tehran would have to adopt "special measures" to protect its nuclear facilities and materials if the threats persist, and the International Atomic Energy Agency would subsequently be informed of the appropriate steps.
Although Araqchi did not specify what measures were being considered, in April an adviser to Iran's supreme leader said that Tehran could suspend cooperation with the IAEA or transfer enriched uranium to safe and undisclosed locations.
Separately, Iran's elite Revolutionary Guards warned that Israel would receive a "devastating and decisive response" if it attacked Iran.
"They are trying to scare us with war, but their calculations are wrong, as they are unaware of the powerful popular and military support that the Islamic Republic can muster in a war situation," the Guards spokesman said. Alimohammad Naini.
The failure of US-Iran talks or a new nuclear deal that does not ease Israeli concerns that Tehran is developing nuclear weapons could be a motive for Israel to strike its arch-rival.
On Tuesday, Iranian Supreme Leader Ayatollah Ali Khamenei said US demands that Tehran halt uranium enrichment were "excessive and outrageous" and expressed doubt that talks on a new nuclear deal would succeed.
Tehran insists its nuclear energy program is solely for civilian purposes.