Pro-Russian activists on Wednesday stormed the Ukrainian navy headquarters in Crimea, media reports said, a day after Russia signed an accession treaty with the leaders of the Black Sea peninsula, dpa reported. The activists took down the Ukrainian flag and replaced it with Russia's, the Russian Interfax news agency reported. Russian Black Sea Fleet commander Alexander Vitko reportedly negotiated with base commander Sergei Gaiduk, but left shortly afterwards. The Russian fleet is headquartered in the port city upon a lease agreement with Ukraine.