Several hundred pro-Russian supporters demonstrating in front of the Ukrainian naval headquarters in Sevastopol broke through the perimeter fence Wednesday, Russian state media said.
They forced their way onto the premises and replaced flags on the masts with the Russian and St. Andrew's flag, Russia's official Itar-Tass news agency reported. The St. Andrew's flag is the naval flag of the Russian Federation, CNN reported.
The incident comes a day after a member of the Ukrainian military was killed, another wounded and more captured when masked gunmen seized their base near the Crimean regional capital, Simferopol.
Tuesday saw Russian President Vladimir Putin announce the annexation of Crimea, after voters in that semiautonomous territory approved a hastily called weekend referendum on separating from Ukraine.
The vast majority of residents of Crimea - 96 percent - voted to secede from Ukraine and join Russia, in a referendum held March 16.
With the exception of Russia most countries refused to recognize the referendum and its results.
A change of power took place in Ukraine on Feb.22.
The Verkhovna Rada (parliament) ousted President Viktor Yanukovych from the power, changed the constitution and scheduled presidential elections for May 25. Yanukovych said that he was forced to leave Ukraine under the threat of violence, and he remains the legally elected head of state. A number of provinces in eastern and southern Ukraine, as well as the Crimea did not recognize the legitimacy of the Rada and decided on possibility of holding a referendum on the future fate of the regions.