People in helmets (left and right), dressed as Russian factories workers, hold a man wearing Barack Obama's mask with mock NATO's bomb in chains, as they take part in a Communists demonstration in downtown Moscow, Russia, Thursday, May, 1, 2014. Thousands of Communists, members of Russia's main political parties and opposition activists staged competing marches in Moscow and other cities Thursday marking the traditional May Day holiday. Poster at the background reads : Peace, Labour, May. (AP Photo/Denis Tyrin)The Associated Press

WASHINGTON The United States and some of its NATO allies see Russia's intervention in Ukraine as a post-Cold War turning point, possibly ending two decades of hope that Moscow could be made a lasting security partner.

NATO's deputy secretary general, Alexander Vershbow, said Thursday that the alliance is compelled to view Russia as an adversary in light of its annexation of Crimea and its apparent efforts to further destabilize eastern Ukraine.

Vershbow, a former U.S. ambassador to NATO and onetime Pentagon official, said Russia's interventionist stance of late poses "grave challenges" to global security arrangements that have developed since the end of World War II.

"What the Russians have done ... is effectively overturned a lot of the pillars of the international security system that we've come to know and be comfortable with," he said.

With the Ukraine crisis and NATO's deteriorating relations with Moscow as a backdrop, Defense Secretary Chuck Hagel was to deliver a speech Friday on the future of the Western alliance and how it can maintain its relevance.

Hagel was expected to argue that the crisis in Ukraine represents a "coalescing moment" for the alliance that should be used to improve NATO defense capabilities, according to an official familiar with his speech preparation.

Fear of Russian aggression is most acute among newer NATO members such as Poland and other Eastern European states that once were part of the Soviet sphere of influence but chose to join the Western alliance after the breakup of the Soviet Union in 1991. Some older NATO members in Europe are less alarmed and see less urgency in trying to punish Moscow for its moves in Ukraine.

In his speech, Hagel also was expected to draw linkages between military security and economic security, in Europe and more broadly, the official said. The official spoke on condition of anonymity because the remarks were still being prepared.

Sen. Carl Levin, chairman of the Senate Armed Services Committee, said Thursday that after a recent trip to Ukraine he believes Washington needs to stiffen its support for the Ukrainian government in its confrontation with Moscow.

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NATO official: Russian moves in Ukraine pose 'grave challenge' to global security system