The Feodosia base in Crimea has been taken by Russian forces, who assaulted the site from two directions using automatic guns and stun grenades, according to Ukraine’s defense spokesman. Russian forces were also using helicopters in the attack.

Ukrainians at the base were rounded up and had their hands tied, and one source told the BBC that shots had been fired.

Elsewhere, NATO’s top military officer announced that Russia may have made Moldova, another ex-Soviet country, as a possible next target. The speaker of Transdniestra’s parliament has asked Russia to incorporate the region.

Breedlove said NATO was very concerned about the threat to Transdniestria, which declared independence from Moldova in 1990 but has not been recognized by any United Nations member state. About 30 percent of its half million population is ethnic Russian and more than half of the total speak Russian as a mother tongue.

Russia has 440 peacekeepers in Transdniestria plus other soldiers guarding Soviet-era arms stocks. It launched a new military exercise, involving 8,500 artillery men, near Ukraine’s eastern border 10 days ago.

“There is absolutely sufficient (Russian) force postured on the eastern border of Ukraine to run to Transdniestria if the decision was made to do that, and that is very worrisome,” Breedlove said.

According to Russian officials, 189 Ukrainian military units and facilities in Crimea are now bearing the Russian flag.