U.S. President Barack Obama has joined German Chancellor Angela Merkel in saying that the West should take a patient, long-term approach to dealing with Russia's aggression in Ukraine.

The real message to Kiev: You're on your own in fighting pro-Russian rebels and Russian troops.

Obama, in an interview on Sunday with CNN's Fareed Zakaria, said the West's limited arsenal prevented it from taking on Russian President Vladimir Putin. "Given the size of the Russian military, given the fact that Ukraine is not a NATO country, and so as a consequence there are clear limits in terms of what we would do militarily, Mr. Putin has not been stopped so far," he said.