The Russian army surrounded a military base in Ukraine in this morning, placing hundreds of soldiers outside a base in Perevalne, in the Crimea region.
The move comes just a day after the Russian parliament approved the use of military force to "protect Russian citizens" in Ukraine.
The military base was one of several outposts surrounded and told to disarm. Some refused leading to stand-off, although no shots have been fired.
Europe Editor James Mates reports from outside the base.
In the nearby port of Sevastopol, the head of Ukraine's navy surrendered his headquarters during a similar blockage.
He was shown on Russian television defecting, and swearing allegiance to the pro-Russian regional leaders of Crimea.
Ukrainian authorities said he was fired for treason, shortly after the footage emerged. Viktoria Syumar, deputy secretary of Ukraine's Security Council said:
During the blockade by Russian forces of the central headquarters of the navy, he declined to offer resistance and laid down his weapons. "The prosecutor's office has opened a criminal case against Denis Berezovsky under statute 111: state treason.
Another admiral, Serhiy Hayduk, has been placed in charge of the navy.