Russian troops -- using stun grenades and firing automatic weapons -- have forced their way inside a Ukrainian marine base in Feodosia.
There were no reports of injuries during the raid early on March 24.
The base was one of the few military facilities still flying the Ukrainian flag in Crimea.
A Ukrainian military spokesman in Crimea, Vladislav Seleznyov, said the Feodosia compound is "full of Russian troops," who were assisted by helicopters and armored personnel carriers.
Seleznyov said on his Facebook page that Russian forces tied up the hands of an unknown number of Ukrainian marines, who were then transported off the base.
Russia has been taking control of military bases across Crimea and stormed two more Ukrainian military installations over the weekend.
On March 23, Russia's Defense Ministry said the Russian flag is now flying over 189 military installations in Crimea.
Based on reporting by Reuters, AFP, BBC, and Channel 5