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"He was convicted for his opposition to Russia's attempted annexation of Crimea and given a harsher sentence than the Russian occupation prosecutor requested," the U.S. diplomats say.

The U.S. State Department added that this "compounds past injustices in the case, including his confinement for several weeks of punitive psychiatric treatment in 2016."

Read alsoRFE/RL: European lawmakers to consider resolution on 'rights abuses' in Crimea"We call on the Russian occupation authorities to immediately release Umerov and vacate his conviction," reads the statement.

The U.S. Department of State reiterated Washington's position on non-recognition of the Russian occupation of the Crimean peninsula.

Read alsoEU: Sentencing of Crimean Tatar leader Umerov is serious violation of human rights"Crimea remains an integral part of Ukraine, and the United States remains steadfast in its support for the territorial integrity and sovereignty of Ukraine," the statement reads.