CNN is reporting that hundreds of troops wearing no insignia but arriving in trucks bearing Russian license plates, have surrounded 3 Ukrainian military bases in the Crimea.

So far, no shots have been fired.

Meanwhile, the Ukrainia government is mobilizing its army, calling up its reserves as the new Prime Minister Arseniy Yatsenyuk warned his country was "on the brink of disaster."

Ukraine's shaky new government mobilized troops and called up military reservists Sunday, even as the defense minister said Kiev stood no chance against Russian troops in a rapidly escalating crisis that has raised fears of a conflict.

Amid signs of Russian military intervention in Ukraine's Crimean peninsula, Russian generals led their troops to three bases in the region Sunday demanding Ukrainian forces surrender and hand over their weapons, Vladislav Seleznyov, spokesman for the Crimean Media Center of the Ukrainian Defense Ministry, told CNN.

Speaking by phone, he said Russian troops had blocked access to the bases, but added "there is no open confrontation between Russian and Ukrainian military forces in Crimea" and that Ukrainian troops continue to protect and serve Ukraine.

"This is a red alert. This is actually a declaration of war in our country," Yatsenyuk said.

Speaking in a televised address from the parliament building in Kiev, Yatsenyuk called on Russian President Vladimir Putin to "pull back the military and stick to international obligations."

"We are on the brink of disaster," he said.

In Brussels, Belgium, NATO ambassadors were scheduled to hold an emergency meeting on Ukraine.

"What Russia is doing now in Ukraine violates the principles of the U.N. charter," NATO Secretary General Anders Fogh Rasmussen told reporters.

"Russia must stop its military activities and threats," Rasmussen said, adding, "we support Ukraine's territorial integrity and sovereignty. ... We support the rights of the people of Ukraine to determine their own future without outside interference."

I doubt whether those words are being heard in Moscow.

Putin is keeping his options open in Ukraine, not even formally acknowledging a Russian military presence in the country. He may feel like negotiating a Ukrainian pullout and recognition of Crimean independence. Or he may not. He might simply take what is easily taken and move on, leaving Ukraine to pick up the pieces.

Either way, its' clear that the decision about whether blood will be shed is entirely up to Vladimir Putin.