A Canadian frigate with 250 marines on board set off from Halifax on the Atlantic coast to join NATO forces in the Mediterranean Sea monitoring the Ukraine crisis.
The Kremlin branded the expansion of NATO as a fundamental threat to Russia in a revised military doctrine that dramatically reflects deteriorating relations with the West.
Ukraine took a historic step toward NATO in a parliamentary vote that stoked Russia's anger ahead of talks on ending the ex-Soviet state's separatist war.
Ukraine's president openly challenged the Kremlin by submitting a bill allowing the former Soviet republic to join NATO and make the Western alliance its defender.
Recent close shaves between Russian fighters and civilian aircraft highlight the dangers of the cat-and-mouse game being played out between Moscow and the West.
NATO's top military commander said he was "very concerned" that Russia's military build-up in the annexed Crimean region could be used as a launchpad for attacks.
NATO accused Russia of sending tanks, troops to east Ukraine, raising fears of renewed all-out fighting and calling into question the Minsk peace deal.
NATO member Poland invited manufacturers of short-range surface-to-air missiles for technical talks for a planned military revamp amid heightened tensions with Russia.
NATO reported more Russian military flights and interceptsover the Baltics, North Sea and Atlantic, just days after it picked up "an unusual level" of activity over European airspace.
NATO said it had tracked and intercepted four groups of Russian warplanes "conducting significant military manoeuvres" in European airspace over the past two days.