Russian troops near the Ukrainian border will return to its permanent bases after completing its military exercises, Russia's Foreign Minister Sergei Lavrov has said, calling for a "de-escalation" of rhetoric.
Russian troops took over a Ukrainian marine base in Feodosia early on Monday, one of the few military facilities that was still flying a Ukrainian flag in Crimea after Russia's annexation, a Ukrainian serviceman said.
First Lieutenant Anatoly Mozgovoy told Reuters on the phone from inside the base that there were shots fired and that the Ukrainian soldiers were unarmed. Asked if the base had been taken over, he said: "Yes".
Vladislav Seleznyov, a Ukrainian military spokesman in Crimea, earlier said Russian forces had been forcing their way in and were assisted by helicopters.
An unusually frank Nato Secretary General issued an unequivocal warning on the course of events should Russia attack Latvia or Estonia.
The West responds with sanctions and closer political ties with Ukraine as Russia's President seals the annexing of Crimea to much fanfare.
Supporters of the controversial fracking industry believe shale gas could be America's most potent weapon in the stand-off with Russia.