Former GOP presidential nominee Mitt Romney on Sunday accused President Obama of being “naïve” about Russian President Vladimir Putin's agenda and said he lacks the foresight to have prevented Putin from taking over a Ukraine peninsula.

"There's no question [about] the president's naiveté with regards to Russia," he said on CBS’ “Face the Nation.” “And his faulty judgment about Russia's intentions and objectives has led to a number of foreign policy challenges that we face.”

During Romney’s 2012 presidential race against Obama, the president criticized him for saying Russia -- not Al Qaeda -- was America's "number one geopolitical foe."

“This is not fantasy land,” Romney, also a former Massachusetts governor, said Sunday. “They are not our enemy but an adversary on the world stage.”

He also said the United States should have worked sooner with allies to make clear the penalties that Russia could have faced if it moved into Ukraine.

The political uprising in Ukraine started about three months ago and included citizens last month ousting their Moscow-backed president.

Russian troops began moving into the neighboring Crimea region of Ukraine about three weeks ago and on Thursday officially annexed Crimea.

“This shouldn’t have been a surprise,” Romney said, referring in part to unmarked Russian troops and military vehicles entering the region days before the takeover. “This had been prepared for some time.”

Romney acknowledged that more pre-emptive action had only the potential to prevent the invasion.

But he also blamed of Secretary of State John Kerry and former secretary Hillary Clinton, suggesting that the Obama administration’s so-called “reset” diplomacy was a mistake.

"They thought resetting relations with Russia, handing out gifts to Russia, would somehow make Russia change its objectives. Well, that certainly wasn't the case," Romney said. “Russia is not our friend.”

He also called for tougher sanctions against Russia, no cuts to the U.S. military budget and re-installing missile-defense systems in Poland and the Czech Republic. He called their removal in 2009 a “gift to Russia.”

The Associated Press contributed to this report.