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 attacked the base from two directions using automatic weapons and stun grenades.
He said they rounded up the Ukrainians and tied the hands of their officers.
Russia has taken over most of Ukraine’s military bases in Crimea, tightening its grip on the peninsula.
A soldier at the Feodosia base told Reuters news agency that shots had been fired and confirmed that the base had been taken over.
Feodosia was one of the last remaining bases under Kiev’s control, but had been surrounded by Russian forces for some time, says the BBC’s Mark Lowen in Crimea’s capital Simferopol.
Overnight on Friday two other military bases were stormed and seized.
Russian defence officials said earlier that the tricolour of Russia had been hoisted at 189 Ukrainian military units and facilities in Crimea.
In other developments:
- 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
- Several parts of Crimea were hit by power cuts on Sunday evening, which officials blamed on technical problems
Russia annexed Crimea following a Moscow-backed referendum on 16 March.
Moscow was angered 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.