SEVASTOPOL (AFP) - Pro-Moscow activists overran the Ukrainian navy's headquarters in Sevastopol on Wednesday with no shots fired, Ukrainian navy spokesman Sergiy Bogdanov said.

"There are about 200 of them, some wearing balaclavas. They are unarmed and no shots have been fired from our side," Mr Bogdanov said.

"The officers have barricaded themselves inside the building and negotiations are ongoing," he said.

"Even though we have the authorisation to use weapons in self-defence, we are not doing so and will not do so," he said.

A report on Russia's state news agency ITAR-TASS said that the activists had raised a Russian flag over the naval headquarters.

The report said the activists had been protesting outside the navy base and then broke in by cutting through the fence.