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President Obama's former Secretary of Defense Robert Gates said Sunday he did not think Russia would relinquish control over Ukraine's Crimea region any time soon. In an interview on Fox News Sunday, Gates said Russia's invasion of the region was "part of a long-term strategy " by Moscow to "create a Russian sphere of influence, a Russian bloc."

"I do not believe that Crimea will slip out of Russia's hand," he said. When host Chris Wallace followed up by asking if he thought Crimea was "gone," Gates responded, "I do."

"I don't think [Russian President Vladimir Putin] will stop in Ukraine until there is essentially a pro-Russian government in Ukraine, in Kiev," he later added.