NATO orders military planners to boost defences and reassure nervous eastern European countries.
NATO says it is also suspending military and civilian co-operation with Russia over its annexation of Ukraine’s Crimea region.
The ‘tough response’ comes as foreign ministers of the 28-nation alliance met for the first time since Russia’s intervention in Crimea triggered the worst East-West crisis since the Cold War.
Russia’s actions meant there could be no “business as usual”.
NATO Secretary-General Anders Fogh Rasmussen said “Russia’s aggression against Ukraine is the gravest threat to European security in a generation and it challenges our vision of a Europe, whole, free and at peace.”
However, despite the uncompromising stance NATO’s chief stressed the “only” path to follow was the political and diplomatic one.