This week, NATO and the U.S. sent a letter of reply to Moscow's security demands. U.S. Secretary of State Antony Blinken said Washington made no concessions, but said the move offered a new "diplomatic path" out of the Ukraine crisis, Deutsche Welle reported.

"Putting things in writing is... a good way to make sure we're as precise as possible, and the Russians understand our positions, our ideas, as clearly as possible. Right now, the document is with them and the ball is in their court," he told reporters.

The letter will not be made public, "because we think that diplomacy has the best chance to succeed," Blinken said. 

But Russia must also play by the rules, Luik told ETV's current affairs show "Aktuaalne kaamera" in Brussels.

"If the Russians want some kind of dialogue, they must start simultaneously bringing their troops home from around Ukraine, because it is absolutely clear that no serious dialogue will be possible while Ukraine is directly threatened," he said.

Although the NATO allies have clearly expressed moving forward with dialogue, Russia has mobilized more forces to the border in recent weeks and planned joint military drills with Belarus.

He said Russia has moved "very modern equipment" such as Iskander missiles or S-400 anti-aircraft systems.

Russia has been massed more than 100,000 troops and military equipment on the border with eastern Ukraine over recent months leading experts to believe a further invasion of the country is imminent.

Last year, Russia demanded NATO roll back its border to how it was in 1997 - before the Baltics, Poland, Romania and Bulgaria joined the alliance.

It also wants NATO to promise to not admit future members and rule out Ukraine and Georgia joining. This goes against the alliance's "open door" policy.

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