Dmitry Levin was charged with contacting the Russian Volunteer Corps, a unit of Russian nationals fighting for Ukraine classed as a “terrorist” organisation by Moscow, and the Ukrainian military intelligence service.

He was accused of sending them information on the movements of Russian ships in the Black Sea port of Novorossiisk in the Krasnodar region, as well as photos of the vessels, the state news agency said.

A military court in the city of Rostov-on-Don found him guilty of treason and of belonging to a “terrorist” organisation, it said.

Since the start of Moscow’s military offensive on Ukraine in February 2022, large numbers of people have received heavy sentences on charges of treason, terrorism, sabotage and spying.

Thousands of people have been penalised, threatened or imprisoned for opposing the conflict.