NATO has not seen any evidence of Russia pulling back troops from the Ukraine border after Russian President Vladimir Putin ordered a withdrawal, NATO Secretary General Anders Fogh Rasmussen said on Monday.

According to Russian officials, President Putin ordered the defense minister to return the troops to their permanent bases.

However, Rasmussen claimed Russia's actions had had a negative effect on Ukraine. "Russia's aggression against Ukraine has challenged the right of states to chose their own path," he said.

Talking about the upcoming Ukrainian presidential elections, he stressed the importance of its accordance with international laws and standards.

"This is the vote that counts for Ukraine and the international community," he said.

On May 25, Ukraine will hold early presidential elections, which the eastern regions of Donetsk and Lugansk have refused to recognize.

Rasmussen said the alliance had taken immediate measures to consider a readiness action plan to strengthen a so-called "response force" to respond quickly to threats.

"We have all plans in place to ensure effective protection of all allies including the Baltics and the means to do it," he said.

"We see a completely new security situation in Europe, less predictable and more dangerous. This has implications now and for the future," Rasmussen added.

NATO on April 16 agreed on a package of extra military measures to reinforce the alliance's collective defence in wake of the crisis in Ukraine, which include enhanced exercises, updated defence plans and appropriate deployments.