"I'm afraid that we probably are past the point where there is any meaningful alternative other than military action to stop the Iranians if they are determined to go ahead. And I don't see that as a possibility," David Kay, who led the US search for weapons of mass destruction in Iraq following the 2003 invasion, said on Sunday.
"My great fear is indeed we will have to learn to leave Iran, and all its terrorist connections, with the bomb," Kay told NBC television's Today Show while declining to say for certain that Iran is seeking nuclear weapons.
Kay ran the Iraq Survey Group that concluded that Iraq had no chemical, biological or nuclear weapons, even as the White House continued to insist that Iraqi leader Saddam Hussein had been a growing threat at the time of the US invasion.
Calling the Tehran regime "toxic", Kay said on Sunday that the tensions over Iran's nuclear power programme - which the US believes masks an intention to develop atomic weapons - differ from those which preceded the US attack on Iraq.
"This time we have a far more united multilateral coalition against Iran and we actually have the International Atomic Energy Agency condemning Iran for 18 years of cheating on its non-proliferation obligations," Kay said.
However, he said, the coalition is far from agreed on the actions to take against an Iraq that has rejected pressures to shut down its uranium enrichment programme, which it claims is for peaceful purposes.
The reactor building of Iran's
Bushehr nuclear power plant
Kay said Europeans in the coalition were particularly bothered by aggressive statements from US leaders threatening tough UN sanctions or worse against Iran.
"When you've got in Tehran a regime that is toxic in the extreme, you really don't need to make the point that there are serious consequences. Everyone knows where we are moving," he said.
Kay, who was the chief UN weapons inspector from 1983 to 1992, would not say for certain that Iran was seeking to build nuclear weapons. "Intentions - that's always the weakest link in intelligence, and it certainly is in this case," he said.
"What you can say right now is Iran has taken a number of steps that are preparatory to having a nuclear weapon. You cannot say that in fact they definitively made that decision to go ahead with that weapons programme."