During a visit to Estonia, like Ukraine a former Soviet republic, Secretary-General Anders Fogh Rasmussen also said there's no "visible evidence" of Russian claims of a troop withdrawal from the border with Ukraine.
"We've seen such announcements also in the past, without any withdrawal of Russian troops so we're very cautious," the Dane told reporters after a speech in the capital, Tallinn.
"I would be the first to welcome it if Russian troops were pulled out, if we see a clear and meaningful withdrawal, because it would contribute to de-escalate the crisis." Asked about Putin's first visit to Crimea since the region became part of Russia, Fogh Rasmussen noted that NATO doesn't recognise the annexation.
In his speech, the NATO chief accused Russia of destabilizing the security situation in Europe.
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"My first message is to Russia. Step back from the brink," he said. He also reassured Estonia and Baltic neighbors Latvia and Lithuania that as NATO members they can count on the alliance's "rock solid" commitment to defend them.
In the wake of the Ukraine crisis NATO has boosted its air patrols and naval presence in the three Baltic countries, which joined NATO in 2004 despite Russian objections.
"And we clearly see such a threat now," he said.