MOSCOW — The European Parliament on Thursday awarded a prestigious human rights prize to a Ukrainian prisoner serving a 20-year term in a penal colony in Siberia, drawing renewed attention to political detainees in the far-flung prison system once known as the gulag.

The award, the Sakharov Prize for Freedom of Thought, is an embarrassment for the Russian government but also elevates the prominence of the prisoner, Oleg G. Sentsov, raising his value in a possible prisoner exchange.

The Russian authorities detained Mr. Sentsov, a movie director, in Crimea in 2014, soon after the Russian military seized the peninsula. He was accused of plotting to blow up bridges, power lines and a statue of Lenin.

Mr. Sentsov denies plotting violent actions, but openly admits opposing Russia’s annexation of Crimea. He went on a hunger strike over the summer and was kept alive for 145 days by medical intervention.