Russian President Vladimir Putin (Photo:  AFP/VNA)

In late February, Putin signed a decree approving the re-establishment of the Moscow and Leningrad military districts to strengthen Russia's northwestern military forces in response to NATO's northern expansion.

On Monday, Sweden officially became the 32nd NATO member, abandoning its long-standing non-aligned military policy. Finland joined the military alliance last year. These two countries used to be considered a buffer zone between NATO and Russia.