Russia's envoy to NATO Alexander Grushko called for a bilateral diplomatic discussion regarding the situation in Ukraine on Friday.

''NATO has increased the regime of air monitoring in the Baltic countries and performs flights in a close proximity to our strategic centers, including St. Petersburg,'' he said, as reported by TASS information agency.

Grushko further elaborated that Russian aviation flights over neutral waters have increased slightly, as compared to the doubling of those by NATO forces, reaching close to 3,000 in 2014.

Additionally, the discussions on possible US arm supplies to Ukraine, have been received with a high dose of concern.

Vladimir Chizhov, Russian ambassador to the EU, pointed out that such an action ''will lead to an escalation of confrontation, to further casualties.'' He further stated that the responsibility for conflict escalation will be held upon those ''pouring oil into the fire.''

A statement has been published in the New York Times, according to which US President Obama has made no decisions on providing lethal assistance.

Russian Foreign Ministry's Spokesperson Alexander Lukashevich has also warned the US against possible deployment of military armaments now being withdrawn from Afghanistan, as this could further trigger a new wave of the civil war in Ukraine.

Meanwhile, Jens Stoltenberg, NATO's Secretary General, said on Thursday that the measures taken in response to Russia's annexation of Crimea can be deemed ''the biggest reinforcement of our collective defense'' since the end of the Cold War, Reuters reported.

At their Thursday meeting, NATO defense ministers made official the decision if situating six command centers across the eastern border of the organization, in Bulgaria, Estonia, Latvia, Lithuania, Poland and Romania.