During a campaign speech on foreign policy at New York University, Biden said President Obama was following a "speak softly and carry a big stick" approach.
"I promise you," Biden said, "the President has a big stick. I promise you."
The comment drew laughter from the crowd of 500, mostly college students.
"President Obama understands what Gov. Romney apparently doesn't: It is possible - it's indeed necessary - for America to be strong and smart - and smart - at the same time," Biden said.
The presumptive GOP nominee has called for a more aggressive stance toward Iran, which is accused of pursuing nuclear weapon capabilities in defiance of international mandates.
"I think it's fair to say - the only step we could take that we aren't already taking is to launch a war against Iran. If that's what Governor Romney means by a very different policy, he should tell the American people," Biden said. "He should say so. Otherwise, the governor's tough talk about military action is just that - talk. And, I would add, counterproductive talk."
Romney adviser Dan Senor told reporters before Biden's speech that the former governor was "not suggesting the military option should be used" against Iran. "We are simply saying the threat needs to be credible for the Iranians to take us seriously," he said.