By Mick Krever, CNN

NATO Secretary-General Anders Fogh Rasmussen told CNN’s Christiane Amanpour in an exclusive interview on Monday that he is “concerned about Russian military activities along the borders of Ukraine.”

Amanpour asked Rasmussen if he was worried that Russia may be “stirring up trouble” in eastern Ukraine as a pretext for intervention. U.S. Secretary of State John Kerry on Friday warned of “continuing provocations” in Eastern Ukraine.

“Absolutely,” Rasmussen said. “That is a possibility, that is a clear risk that would further deteriorate the whole situation.”

NATO worried about more Russia intervention Click to watch video

With more than 20,000 Russian soldiers in Crimea, according to the interim Ukrainian government, Crimeans voted overwhelmingly to leave Ukraine and join Russia.

Crimea's Moscow-backed leaders declared that an overwhelming 96.7% voted in favor of being annexed by Russia, in a vote that Western powers said was illegal. Turnout was 83%.

“It is a Russian attempt to redraw the map, the European map, to create new dividing lines in Europe. So a lot is at stake.”

NATO: No de-escalation in Ukraine Click to watch video

Rasmussen reiterated that military intervention is not a solution to the crisis. Ukraine is not a NATO member.

“To be very honest about it, right now I don’t see any de-escalation. On the contrary, I see Russian military build-up and this is a matter of concern.”