Nato has decided to reinforce its forces in eastern Europe "immediately" as a result of the crisis in Ukraine, Secretary General Anders Fogh Rasmussen has said.
"You will see deployments at sea, in the air, on land to take place immediately, that means within days," Mr Rasmussen told a news conference.
The move means Nato fighter planes will fly more sorties over the Baltic region, with ships being sent to the Baltic sea and the eastern Mediterranean.
Tensions remain high in eastern Ukraine after at least three died in a day of shooting during what was supposed to be an Easter truce.
In an exclusive interview with NBC News, the Ukrainian Prime Minister warns of the dangers of unchecked Russian expansion and aggression.
Russia, the US and the EU say that all sides have agreed to steps to "de-escalate" the crisis in Ukraine at talks in Geneva.