Marseille: NATO chief Anders Fogh Rasmussen said in an interview published on Sunday that the alliance would draw up new defence plans in the face of "Russia`s aggression" against Ukraine, urging members to up their military spending.
Echoing comments by British Prime Minister David Cameron, Rasmussen told French regional newspaper Midi Libre that "Russia`s aggression was a warning and created a new security situation in Europe".
"We will strengthen military exercises and prepare new defence plans," he said.
"I will encourage NATO countries to increase their defence investments. Over the past five years, Russia has increased its spending on defence by 50 per cent, and NATO countries have reduced theirs by an average of 20 per cent," he added.
"We must reverse the trend."
Russian support for pro-Kremlin separatists in eastern Ukraine has angered Europe and the United States, and the downing last month of Malaysia Airlines flight MH17 over territory held by the rebels brought the crisis to a head.
For the first time, sanctions imposed by Brussels and Washington against Russia last week applied to entire sectors, impeding access to Western capital markets and technology needed to develop new oil and gas fields, as well as imposing an arms sales ban.
Cameron yesterday also called on NATO to rethink its long-term relationship with Russia and strengthen its ability to respond quickly to any threat, in a letter to Rasmussen and leaders of the 27 other member countries.
"We must accept that the cooperation of recent years is not currently possible because of Russia`s own illegal actions in NATO`s neighbourhood and revisit the principles that guide our relationship with Russia," he wrote.
Rasmussen agreed, telling Midi Libre that Russia considered NATO a foe.
"I regret this because we must develop a fruitful cooperation between the West and Russia. But we have to adapt to this new situation," he said.
The NATO chief also said that the downing of flight MH17 was a "war crime."
"We have a lot of information that the separatists, supported by the Russians, are guilty," he said.