The new "high-readiness spearhead force" is in place for 2015, Stoltenberg said after calling on Russia to respect the sanctity of postwar borders in Europe and the core values on which the continent's democracies are based.
It was Russia's annexation of Ukraine's Crimea peninsula 10 months ago that prompted the Western defense alliance to create the force capable of responding quickly to any threat to one of the bloc's 28 member states.
Stoltenberg did not disclose the number of troops assigned to the NATO Response Force, which for the current year will be headquartered in Muenster, Germany.
FOR THE RECORD
Jan. 15, 8:35 a.m.: An earlier version of this article stated that the rapid-reaction force was already deployed to Eastern Europe states. Troops remain at their national bases.
The ultimate size of the force will be "several thousand troops" able to respond within a few days to any attack or security threat, NATO spokeswoman Oana Lungescu said.
Ukraine is not a member of NATO and it pledged in 2010 to remain nonaligned. The Ukrainian parliament retracted that position late last year in a signal that it intends eventually to apply for alliance membership.
Russian President Vladimir Putin is staunchly opposed to what he sees as NATO encroachment into Moscow's traditional sphere of influence. He is also clearly displeased with Ukraine's moves toward eventual membership in the European Union. It was after a Kremlin-allied Ukrainian president, Viktor Yanukovich, was ousted by a pro-European rebellion that Russian troops seized Crimea and Russian arms and mercenaries began flowing into eastern Ukraine.
Putin denies Russia is involved in the fighting in Ukraine that has killed more than 4,700 people in nine months, and he has justified the "reunion" of Crimea with the Russian federation as correcting a historical wrong. Soviet leader Nikita Khrushchev deeded the territory that is home to the Russian Black Sea fleet to the Ukrainian Soviet Socialist Republic in 1954.
Stoltenberg alluded to "the challenges we are facing to the east" during a news conference with German Chancellor Angela Merkel.
"We see that international law is violated, and that the sovereignty and the territorial integrity of Ukraine is not respected. And we call on Russia to respect the Minsk agreements," Stoltenberg said.
He was referring to the Sept. 5 cease-fire signed in Minsk, the capital of Belarus, by Russia and Ukraine that set out a plan for halting artillery fire, withdrawing heavy weaponry, freezing the front lines and exchanging prisoners. The agreement has been repeatedly violated and few of its provisions fulfilled beyond a recent exchange of about 370 captives.
"I underline very much that NATO does not seek confrontation with Russia," Stoltenberg said. "NATO aspires for a more constructive and cooperative relationship with Russia. But to be able to establish that, Russia must want it too."
There was no immediate reaction from Russian officials or Moscow's state-run media to the news that the readiness force was in place.
Asked at the news conference whether Ukraine would be granted NATO membership, Stoltenberg said there has been no application made as yet and that Ukrainian officials have conceded it will be years before the internal reforms are completed that are necessary to integrate with alliance defense forces.
But there is "a fundamental principle which all countries in Europe have subscribed to, and also that Russia has supported, and that is that all sovereign nations have the right to choose their own path," Stoltenberg said, adding that any membership bid would be evaluated on the same criteria as applied to other states wishing to join.
Latvia, Lithuania and Estonia -- three Baltic Sea states that were part of the Soviet Union after being invaded and annexed in 1940 -- are already members of NATO and will be among the Eastern European countries to which the new rapid-response forces may be dispatched.
Poland, with its own long history of facing aggression by Russia, has announced a major redeployment of its national defense forces from bases in the western part of the country to fortify positions in the east. Poland shares a 125-mile border with Russia's heavily militarized Kaliningrad exclave, the former German territory of Koenigsberg captured by the Soviet Red Army with the Nazi defeat in World War II.
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