NATO said on Wednesday the military alliance had decided on immediate steps to reinforce its forces in eastern Europe because of the Ukraine crisis.
NATO has made clear it will not intervene militarily in Ukraine despite Russia's annexation of Crimea and a buildup of Russian forces on the Ukrainian border.
But the 28-nation alliance has bolstered its military presence in eastern European member states, including the ex-Soviet republics in the Baltics.
NATO ambassadors agreed on Wednesday on further military steps.
"You will see deployments at sea, in the air, on land to take place immediately, that means within days," NATO Secretary-General Anders Fogh Rasmussen told a news conference after the ambassadors' meeting.
NATO fighter aircraft will fly more sorties over the Baltic region, allied ships will be deployed to the Baltic, the eastern Mediterranean and elsewhere, and allied military staff will be sent out to improve NATO's preparedness for training and exercises, Rasmussen said.
NATO will review and reinforce its contingency plans to defend members of the alliance, Rasmussen said. More steps to reinforce defences would follow, if needed, in coming weeks and months.
Despite calls by some eastern European allies for NATO soldiers to be permanently based on their territory, Rasmussen said NATO had not taken any decisions on Wednesday on permanent bases in the Baltics, but NATO was looking into more medium- and long-term measures to strengthen its defences.
Separatists hoisted the Russian flag on Ukrainian armoured vehicles in eastern Ukraine on Wednesday, mocking the Kiev government's attempt to reassert control on the eve of talks in Geneva on the country's future, amid escalating rhetoric between Moscow and Kiev.