In a way, this was obviously coming.. But it did take a long time, if it's really linked.

There were many concerns that the "No Russian" level in COD6 would incite or facilitate the measures taken my extremists, and it might have taken place recently at a Russian Airport.
http://kotaku.com/5742990/russian-tv-links-modern-warfare-2-to-russian-massacre

Kotaku has more on the link.