A Russian court has convicted a Ukrainian filmmaker of conspiracy to commit terror attacks and sentenced him to 20 years in prison Tuesday raising international concerns about the fairness of the trial. 

The court in the southern city of Rostov-on-Don said Tuesday that Oleg Sentsov had set up a terror cell in the Crimean Peninsula and was plotting attacks.

Sentsov, a Crimean native, was a vocal opponent of Russia's 2014 annexation of the peninsula which followed a hastily called referendum. Critics have dismissed his prosecution as revenge for his pro-Ukrainian position.

"From the outset the in the international community has had concerns about both of the men's access to a fair trial,"  Britain's Foreign & Commonwealth Office said in a statement. "These appear to be disproportionate and politically motivated charges."

Sentsov and Oleksandr Kolchenko have been detained since May 2014.

Sentsov, who didn't apply for Russian citizenship, was grabbed on a street in Crimea's capital in May 2014 by Russian security officers and resurfaced days later in custody in Moscow.

Earlier in the trial, Sentsov had pleaded not guilty and insisted that a Russian court had no jurisdiction.

The Associated Press contributed to this report