Sentsov, a leading Ukrainian director best known for the 2011 film Gamer, was sentenced Tuesday to 20 years at the Rostov-on-Don courthouse.
He was arrested in May 2014, and charged with arson attacks in Crimea, charges which he denied, along with the court's right to charge him with anything as Russia's annexation of the Crimean peninsula was a clear breach of international law.
Another activist, Aleksandr Kolchenko, was sentenced to 10 years in prison on similar charges.
The United States and European Union have both condemned the trial, and on Wednesday Latvia added its voice to the chorus of disapproval for Russia's actions, which are reminiscent of the worst excesses of Stalinist show trials.
The Foreign Ministry described the trial as "a clear violation of international law and human rights."
"It is unacceptable that the Russian Federation carries out a court prosecution for acts [allegedly] performed beyond the jurisdiction of the Russian Federation" said the ministry's statement.
"We call on Russia to immediately release Sentsov and Kolchenko, as well as other citizens of Ukraine who are being illegally detained," the statement concluded.
