Several hundred pro-Russia protesters have stormed the Ukrainian naval headquarters in the city of Sevastopol in the Crimean peninsula.
They had been holding a rally outside the building early on Wednesday morning.
They broke through the fence, forcing their way in, and replaced Ukrainian flags with Russian ones.
A spokesperson for the Ukrainian ministry in Crimea said some of the men and women were masked.
The unrest has prompted Kyiv to send senior Ukrainian officials to Crimea – a move Crimean Prime Minister Sergei Aksyonov said would be rebuffed.
“They are not wanted in Crimea. Nobody will let them into Crimea, they will be sent back,” Interfax quoted Aksyonov as saying.
It comes as an image emerged on Twitter purporting to show a Ukrainian officer leaving a military base under armed supervision.
On Tuesday (March 18), Sevastopol signed a treaty with Moscow to become part of the Russian Federation. The city is home to Russia’s large Black Sea fleet.
Ukrainian officer leaving HQ building in Sevastopol after being stormed pic.twitter.com/87tVoxWSX8— bruce springnote (@BSpringnote) March 19, 2014