Pro-Russian forces besieged Ukrainian military bases in Crimea in two separate incidents on Saturday.

In the first incident, around 200 pro-Russian protesters stormed one of the last Ukrainian-controlled military bases in western Crimea.

The unarmed group broke through the air force base in Novofedorivka, yelling "Russia! Russia!" The attack resulted in the Ukrainian soldiers leaving the base, with protesters taking down the Ukrainian flag, and putting up the Russian navy's flag, according to the AFP.

Ukrainian soldiers surrendered after barricading themselves inside, and throwing smoke bombs at protesters, as Russian officers stood outside watching, the AFP said. Most of the attackers were reportedly non-locals.

"There are some locals among the attackers, but a lot of non-locals. We do not recognize these faces," a source from the base told Vladislav Seleznyov, spokesperson of the Ukraine defence ministry in Crimea.

Russian officers went in to negotiate with the barricaded soldiers, and the Ukrainian soldiers left the base after performing the national anthem, according to the BBC.

Meanwhile, in Belbek, outside of Sevastopol, Russian troops surrounded another Ukrainian airbase. The troops issued an ultimatum — which was set to expire at 7:30 a.m. ET — to the soldiers inside to surrender Reuters reported.

The occupation of the two bases are the latest episodes in the Russian takeover of the Crimean peninsula. Citizens of Crimea voted last Sunday to secede from Ukraine, with an overwhelming 95% of the vote in favor of secession. The U.S. National Security Council denounced the referendum as illegal.

Since then, Russian forces have moved to take control of the region, with Ukrainian forces planning an evacuation. Despite the high-tension situation, the occupation has been mostly bloodless, although two deaths, the first victims of the conflict, were reported on Tuesday.

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