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"When it comes to Ukraine, it was clearly stated by many allies – and the whole Alliance is behind the message – that we are going to continue to strengthen our close partnership with Ukraine to provide practical support, political support," he said following the NATO leaders' meeting in Brussels on Thursday, May 25.

"And there was a strong support, of course, for all efforts to try to make sure that we're really able to implement the Minsk agreements, and especially allowing the international monitors to be able to do their job," he said.

In his words, Russia was also on the agenda of the meeting. "And when we see that Russia is willing not only to invest heavily in defense, but actually use military force to change borders in Europe with its aggressive actions against Ukraine, illegally annexing Crimea and continuing to undermine, to destabilize eastern Ukraine, then, of course, NATO has to react," he said.

Read alsoUkraine's Krasnohorivka under attack: Hospital, university block, houses damagedStoltenberg says no one was thinking about deploying four battle groups to the Baltic countries and Poland before Russia annexed Crimea and started to destabilize eastern Ukraine. "So what NATO does is a defensive, proportionate response to the actions of Russia. At the same time, we're working for dialogue," he said.

"Today we reaffirmed our dual-track approach: strong defense combined with meaningful dialogue. And we are delivering on both tracks. Allies stand strong together not to provoke conflict, but to prevent conflict, and to preserve peace. At the same time, we remain open to dialogue with Russia to increase transparency and reduce risks," he said.

He reiterated that NATO is a defensive alliance, NATO does not see confrontation with Russia. "Actually, we recognize that Russia is our biggest neighbor, and we're striving for better and more constructive relationship with Russia. At the same time, NATO has to deliver credible deterrence and defense. Because by delivering credible deterrence and defense, we're preventing conflict, we're preventing war. That has been a key to success of NATO since we were founded almost 70 years ago," he added.

Read alsoTrump mentions threats from Russia as NATO's focus in futureOn May 25, 2017, Brussels was hosting a meeting of NATO Heads of State and Government. The meeting was chaired by Stoltenberg. It was preceded by the unveiling of two artefacts – German Chancellor Angela Merkel dedicated the Berlin Wall Memorial, and U.S. President Donald Trump the 9/11 and Article 5 Memorial. Also, there was a ceremony marking the handover of the new NATO Headquarters from the Belgian Ministry of Defense.