Former New York City Mayor Rudy Giuliani (R) is taking on the White House for not explicitly threatening a "military strike" on Iran, which he called "magic words" that would prevent the country from obtaining military weapons.

Speaking at the United Nations on Tuesday, President Barack Obama said that containment was not an option and the U.S. would "do what we must" to stop Iran.

But during an interview with MSNBC, Giuliani said that the implicit threat of military force did not go far enough.

"I didn't hear him say the magic words, that he'd use a military strike," Giuliani, who is a surrogate for Republican presidential nominee Mitt Romney, told MSNBC's Chuck Todd.

"When you say containment, do you have to use the phrase, 'military strike'?" Todd wondered.

"Sure, what else does that mean? It could mean even more significant sanctions, really dramatic sanctions, really big sanctions," Giuliani explained. "There's a reason he doesn't use the word 'military strike.' Ronald Reagan certainly wouldn't have shied away from using the word 'military strike.' And I see [Obama] much more like Jimmy Carter making threats that the Iranian regime does not take seriously."