"It's been conclusively proven Iran is not going to be talked out of its nuclear program. So to stop them from doing it, we have to massively increase the pressure.

"If we can't get enough other countries to come along with us to do that, then we've got to go with regime change by bolstering opposition groups... that's the circumstance most likely for an Iranian government to decide that it's safer not to pursue nuclear weapons than to continue to do so. And if all else fails, if the choice is between a nuclear-capable Iran and the use of force, then I think we need to look at the use of force," Bolton told the Telegraph.

The former ambassador, who still holds close ties with US President George W. Bush, pointed out that military action had its disadvantages and may not succeed. "It's very risky for the price of oil, risky because you could take out their enrichment capabilities at Natanz, and they may have enrichment capabilities elsewhere you don't know about."

The risks involved in using force, Bolton said, would be less severe than those of accepting a nuclear Iran. "Imagine what it would be like with a nuclear Iran. Imagine the influence Iran could have over the entire region. It's already pushing its influence in Iraq through the financing of terrorist groups like Hamas and Hizbullah.

"If the choice is them continuing [towards a nuclear bomb] or the use of force, I think you're at a Hitler marching into the Rhineland point. If you don't stop it then, the future is in his hands... just as the future decisions on their nuclear program would be in Iran's hands," he continued.