By RAPHAEL G. SATTER
ASSOCIATED PRESS WRITER 

United States former senator Fred Thompson delivers a speech at the right-wing British think tank Policy Exchange in London, Tuesday, June 19, 2007. The United States will miss Tony Blair, even if the special relationship between the United States and Britain will endure through the leadership changes looming on both sides the Atlantic, U.S. presidential hopeful Fred Thompson said Tuesday. The former senator offered few regrets for the decision to go to war in Iraq and said that both the U.S. and Britain should be prepared to rejoin a "coalition the willing" where the international community had failed to confront aggression, and that neither should be afraid to use the threat of force to back their demands. (AP Photo/Sang Tan)

LONDON -- The threat posed by Iran can only be contained if the use of force is kept on the table, potential presidential candidate Fred Thompson said Tuesday.

Thompson, an actor and former Republican senator from Tennessee, said the U.S. and its allies must ensure that leaders like Iranian President Mahmoud Ahmadinejad "do not gain the capability to carry out their evil ambitions."

"Of course, diplomacy is always to be preferred in our dealings with dangerous regimes," he said. But he added: "The words of our leaders command much closer attention from adversaries when it is understood that we and our allies are prepared to use force when force is necessary."

The United States and some of its allies fear that Iran, under Ahmadinejad's hardline leadership, is using its civilian nuclear program as a cover to produce atomic weapons. Iran denies the charge, saying its nuclear program is geared toward generating electricity.

The Bush administration has said it is committed to using diplomacy to resolve the standoff with Iran, although Vice President Dick Cheney has repeatedly said the U.S. is keeping "all options on the table" in its dealings with Tehran.

Thompson has taken preliminary steps toward a presidential run in 2008. Although he has not formally announced his candidacy, he placed a close third behind former New York mayor Rudy Giuliani and Sen. John McCain in a recent Associated Press-Ipsos poll of Republican hopefuls.

Thompson was in London to address the conservative think tank Policy Exchange. He said he would also meet former British Prime Minister Margaret Thatcher during his visit.