Fox News senior strategic analyst General Jack Keane (Ret.) warned that the current tension between Russia and NATO is reminiscent of the Cold War. On "America's Newsroom" Monday, he said that NATO needs to make clear to President Putin that it will not allow expansion into Ukraine.

WHY PUTIN IS WILLING TO RISK A CATASTROPHIC WAR TO DOMINATE UKRAINE

GEN. JACK KEANE (RET.): The mission of the United States and NATO during the Cold War was to deter Russian aggression and expansion. And if that fails, win a war against the Soviet Union. The mission now of NATO is deter Russian aggression and expansion. It's the same mission. It's just we're not doing it quite as well as we should be doing. Russia put 90,000 troops on Ukraine border in the spring, and we did what? What did NATO do? Nothing.

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We should have put troops into NATO, particularly in Poland and the Baltics to reinforce those countries, make certain that Putin gets the message that we're not going to take any further expansion. And I would have given Putin a laundry list of significant military capacity that I intend to put into Ukraine unless he deescalates and gets those troops off the border.

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Gen. Keane warns NATO currently has 'same mission' as during the Cold War: Deter Russian expansion, aggression

He said on "America's Newsroom" that the U.S. and NATO need to make Putin understand that he cannot expand to Ukraine.