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STORY: "We are not part of this conflict, and we have a responsibility to ensure it does not escalate and spread beyond Ukraine because that would be even more devastating and more dangerous," NATO Secretary-General Jens Stoltenberg told a news conference.

Ukrainian President Volodymyr Zelenskiy has called for Western powers to enforce a no-fly zone since Moscow's invasion started nine days ago, with Russia shelling cities and bringing fighting to Europe's largest nuclear plant.

NATO members have been sending arms to Ukraine, but stopped short of military action that would put them in direct conflict with Russia.

The only way for NATO to implement a no-fly zone would be to send NATO planes to shoot down Russian ones, Stoltenberg said, adding that the risk of escalation would be too big.