Russia's Federal Security Service has arrested a man accused of leaking classified information to the Russian Black Sea Fleet in Ukraine, RIA Novosti reported.
The arrest comes at a time of heightened tensions with Ukraine as Moscow strengthens its military forces near its common border. Russian Defense Minister Sergei Shoigu arrived in Crimea today to oversee large-scale military exercises.
The military exercises will involve at least 10.000 soldiers and more than 40 warships, the defense ministry said, according to the Interfax news agency.
Russia annexed the Crimean peninsula from Ukraine in 2014, prompting the West to impose sanctions. Ukraine wants the region back to its sovereignty.
The man, whose name has not been released, was arrested in Sevastopol for allegedly gathering and passing secret information to Ukrainian military intelligence about the Russian Black Sea-based fleet, security services said.
Many cases of betrayal have been reported in Russia in recent years. Critics of the government have challenged the allegations in some of the cases, saying the allegations could not be substantiated because details of the cases were not disclosed.
Last month, a woman was sentenced to 12 years in prison for spying for Ukraine in a closed-door trial.
Lyudmila Denisova, the ombudsman for human rights in the Ukrainian parliament, said the case against the woman was fabricated.