Russian troops 'overrun Crimea's Feodosia naval base'
Russian troops have seized control of a Crimean naval base at Feodosia, the third such attack in 48 hours, Ukrainian officials have told the BBC.
Defence spokesman Vladislav Seleznyov said the Russians had attacked the base from two directions using armoured personnel carriers and stun grenades.
Russia has taken over most of Ukraine's military bases in Crimea.
The G7 group of industrialised countries is to consider a collective response to the crisis in The Hague.
There is deepening concern here at what is happening in Crimea.
The question is what exactly the Ukrainians can do, what the West can do, at least for the short term, and what Russia's next move will be.
There have been fears that there will be a move into eastern Ukraine. On Sunday, the Nato commander for Europe said that there were many, many troops gathering on Ukraine's border. He said they were "very, very ready" and could go all the way to Moldova, on Ukraine's western border.
There is a recognition that there is not going to be any kind of Western military action. US President Barack Obama has made that clear.
What people seem to be asking for is perhaps more military support. US Senator John McCain has called for help in supplying the Ukrainian military; also bolstering forces around Nato countries on the border with Russia or close to Ukraine.
But the big question really is what could deter Russia at this moment. Moscow seems to be moving ahead at least for the short term with whatever plans it has made.
Leaders of the G7 will hold talks on Monday on the sidelines of a long-planned summit on global threats to nuclear security.
Russian President Vladimir Putin is staying away from the nuclear conference, choosing to send his foreign minister instead.
The Ukrainian defence ministry spokesman told the BBC that Russian troops had rounded up the Ukrainians at the Feodosia base and tied the hands of their officers.
A Ukrainian soldier there told Reuters news agency that shots had been fired and confirmed that the base had been taken over.
The BBC's Mark Lowen in Crimea said Russian troops were now in complete control and the Ukrainian soldiers had been taken away.
Feodosia was one of the last remaining bases under Kiev's control, but had been surrounded by Russian forces for some time, says our correspondent in Crimea's capital Simferopol.
Two other military bases were stormed and seized on Friday.
Russian defence officials said earlier that the tricolour of Russia had been hoisted at 189 Ukrainian military units and facilities in Crimea.
The view in Kiev is one of deepening concern, says the BBC's David Stern in the Ukrainian capital.
The question now, he says, is how Ukraine and the West will respond, and what Russia's next move will be.
Nato's military commander in Europe warned on Sunday that Russian forces on Ukraine's eastern borders were capable of mounting an operation all the way to Moldova.
In other developments:
- Several parts of Crimea were hit by power cuts on Sunday evening, which officials blamed on technical problems
- There is still no confirmation of the whereabouts of Col Yuli Mamchur, the commander of Belbek base, which fell on Saturday. He was taken by Russian forces reportedly to a military prison. The interim Ukrainian president has demanded his immediate release
Russia annexed Crimea following a Moscow-backed referendum in the area on 16 March.
Moscow's move came after protesters overthrew pro-Kremlin President Viktor Yanukovych in February.
The Kremlin said it had acted to protect its "compatriots" in Crimea from "fascists" moving in from the mainland Ukraine.
The US and EU have responded with a series of sanctions targeting those individuals including senior officials that they accuse of involvement in Crimea's annexation.