Republican presidential candidate Mitt Romney called Russia "without question our number one geopolitical foe" Monday on CNN.

Romney's comments came in the context of President Barack Obama's "hot mic" moment with Russian President Dimitri Medvedev Monday after a meeting in Seoul. Obama was heard telling Medvedev he would have "more flexibility" on missile defense after the presidential election.

"This is without question our number one geopolitical foe, they fight for every cause for the world's worst actors. The idea that he has more flexibility in mind for Russia is very, very troubling indeed," Romney said.

Wolf Blitzer asked if he thought Russia was a bigger foe than Iran, China or North Korea.

"I'm saying in terms of a geopolitical opponent, the nation which lines up with the world's worst actors," said Romney. "Of course the greatest threat that the world faces is a nuclear Iran and a nuclear North Korea is already troubling enough."

"But when these terrible actors pursue their course in the world and we go to the United Nations looking for ways to stop them; when [Syrian President Bashir al-] Assad for instance is murdering his own people we go to the United Nations and who is it that always stands up with the world's worst actors, it's always Russia, typically with China alongside," he continued. "And so in terms of a geopolitical foe, a nation that's on the Security Council ... and is of course is a massive nuclear power, Russia is the geopolitical foe."

Romney has consistently criticized Obama over his policy of "resetting" relations with Russia after the two countries' relations reached a nadir in August 2008, at the end of the Bush administration and after the Russia-Georgia War. The U.S. and Russia -- which still have the vast majority of the world's nuclear arms -- agreed to modest nuclear reductions in April 2010 as part of a successor treaty to the START agreement.