Russian Foreign Minister Sergey Lavrov argues that Russia has invaded Crimea and Donbas as a result of NATO's eastward expansion.

"The Ukrainian crisis was not the cause of current relations between Russia and the West, it was rather a consequence of the policy that Western countries, primarily the United States and NATO Allies, conducted after the end of the 'Cold War'," Lavrov said in an interview with the Serbian Beta News Agency, according to the Russian Foreign Ministry's website.

According to him, "instead of taking advantage of the unique historical chance and forming a truly pan-European structure of security and cooperation, the West opted for NATO expansion despite all the promises made by the leaders of the United States and many European countries in 1990 that the Alliance would not advance an inch eastwards."

Read alsoReuters: Ukraine crisis needs 20,000-strong U.N. force: report"It was not written down in any agreements and legal documents (probably, it should have been done), but a so-called 'gentlemen's agreement' was reached, which was, in fact, trampled on by our Western counterparts. Probably, in the future we will try to understand better who a gentleman is, and who is not. But those official documents from the American archives, which were declassified recently, unequivocally show that such strong assurances were given in a dialogue between the Soviet Union and U.S., in contacts between Moscow and Berlin, Moscow and Paris," Lavrov said.

According to him, "what happened in Ukraine was no surprise for Russia."

"This became, as I said, a consequence of the line that NATO had chosen. After the 'Cold War' ended, three waves of the Alliance's expansion took place, and with each such wave its military infrastructure was getting closer and closer to the Russian borders," he said.

Lavrov is convinced that now the Balkans might be drawn into this game, as the Balkan states will be forced to make a choice: either they are with the West or with Russia.

"Making such choice was also demanded from Ukraine," he stressed.