WASHINGTON, United States: 30 US senators wrote to President George W. Bush, warning he had no authority to launch military action against I.R. of Iran, and expressing concern about the administration's "provocative" rhetoric.

The senators, 29 democrats and one independent, urged the resolution of disputes with the Islamic Republic through diplomacy.

"We wish to emphasize that no Congressional authority exists for unilateral military action against Iran," the letter signed by senators including presidential candidates Hillary Clinton and Joseph Biden said.

The letter warned that a resolution passed by the Senate in September, calling for the designation of the Islamic Revolution Guard Corps (IRGC) as a terrorist group, should not be used as a pretext for war.

It hit out at "provocative statements and actions" by the administration on Iran, after Bush last month warned Tehran must be barred from nuclear weapons to avoid the prospect of "World War III."