Pro-Moscow demonstrators in Sevastopol have named a Russian citizen Alexei Chalov as the new mayor of Sevastopol, underscoring fears that the region may try to break away from turmoil-gripped Ukraine, Crimea's Navigator news agency reported.

About 20,000 demonstrators carrying Russian flags gathered in Sevastopol for a rally on Sunday. Demonstrators waved Russian flags – there was not a Ukrainian flag to be seen – and chanted "Russia, Russia, Russia" during the gathering.

"Sevastopol is a Russian town and will always be a Russian town… we will never surrender to those fascists in Kiev," said Anatoly, who was handing out Russian flags and declined to give his surname. "The struggle is only just beginning."

Sevastopol is the only city in Ukraine whose residents do not get to elect their mayor directly as a law on the seaport's municipal governance is yet to be approved by Ukraine's parliament, Sevastopolskaya Gazeta reported, according to Moscow Times.

In the eastern Crimean city of Kerch, protesters tore down the Ukrainian flag from the City Hall and replaced it with the Russian one, reported.

After the rally, many protesters headed to the offices of the Russian Unity organization to enlist in a self-defense force.