At a news conference in Belgium, President Obama said he is concerned not all NATO members are "chipping in" toward the cost of a collective defense and deterrent against Russia.

"The situation in Ukraine reminds us that our freedom isn’t free, and we’ve got to be willing to pay for the assets, the personnel, the training to make sure we have a credible NATO force and an effective deterrent force,” Obama said at the Council of the European Union in Brussels.

Obama didn't specify which countries he was speaking about, but said the monetary commitment can't lie with the largest powers.

"This can't just be a U.S. exercise or a British exercise," Obama said. "Everybody is going to have to make sure they’re engaged and involved."

Obama said neither Ukraine nor Georgia are "currently on the path to NATO membership." However, he said, Russian officials said on background that the potential of NATO membership was one of the reasons they were concerned about Ukraine.