Russia"s Federal Security Service arrested a man in Crimea on Thursday on suspicion of treason for allegedly handing over secret information to Ukraine about Russia"s Black Sea Fleet, the RIA news agency reported. The arrest comes amid acute tensions with Ukraine as Moscow has built up military forces near their shared border. Russian Defence Minister Sergei Shoigu arrived in Crimea on Thursday to oversee large-scale military drills. read more Russia annexed the Crimean peninsula from Ukraine in 2014, prompting the West to impose sanctions. Ukraine wants the region back. The man, who was not identified by name, was arrested in Sevastopol for allegedly gathering and handing over secrets to Ukrainian military intelligence about the Russian fleet that is based on the Black Sea, the security services were cited as saying. There has been a spate of treason cases in Russia in recent years. Government critics have questioned the charges in some of those cases and said the allegations cannot be scrutinised because case details are typically not disclosed. Last month a woman was sentenced to 12 years in jail for spying on behalf of Ukraine at a trial held behind closed doors. read more Lyudmyla Denisova, the human rights ombudsman for the Ukrainian parliament, said the case against the woman was fabricated.