"Let me assure you that if we get visible evidence that they are actually pulling back their troops, I will be the very first to welcome it," NATO Secretary General Anders Fogh Rasmussen said in Warsaw.
"I have to repeat that while we have noticed the Russian statements that they have started to withdraw troops, so far we haven't seen any, any indications that they're pulling back," he said after talks with Polish Prime Minister Donald Tusk.
Putin announced a pullback on yesterday in response to Western concerns of a possible Ukraine invasion, but both the Western military alliance and the United States have questioned the claim.
"For those with a blind eye we suggest to follow President Putin's statement of May 7," Russia's foreign ministry said on Twitter after Rasmussen tweeted that he saw no sign of a withdrawal.
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Asked about the Russian tweet by reporters in Warsaw, Rasmussen responded: "I have very good vision."
The 28 members of the North Atlantic Treaty Organisation have responded to Russia's intervention in Ukraine by stepping up defences in Eastern Europe, sending warships, fighter jets and troops to the region.
The troop surge is scheduled to end on December 31, but the alliance has said the build-up could become permanent.