A Ukrainian filmmaker who has been in a Russian jail for more than a year on Tuesday pleaded not guilty to charges of conspiracy to commit terrorism.

Critics have dismissed Oleh Sentsov's prosecution as revenge for his pro-Ukrainian position in Russia-occupied Crimea. Sentsov, a Crimean native, was a vocal voice against Russia's annexation of Crimea which followed a hastily called referendum in March.

The 39-year-old Sentsov was arrested in Crimea's capital in May 2014 after a pro-Ukrainian rally protesting the annexation.

At the opening of his trial in the southern city of Rostov-on Don on Tuesday, Sentsov pleaded not guilty and insisted the case against him is a fabrication, Russian news agencies reported.

Sentsov's defense team describes Sentsov's arrest in May 2014 as a kidnapping.

Sentsov, who unlike many Crimeans didn't apply for Russian citizenship, was grabbed on the street in Crimea's capital, Simferopol, by Russian security agents and resurfaced days later in custody in Moscow.