Legendary filmmaker Alexei German died Thursday at the age of 74.
The cause of his death was not immediately known, but his son wrote on his Ekho Moskvy blog that his father's "heart simply stopped."
A later report from RIA-Novosti cited kidney failure as the cause of death.
He died at a hospital in St. Petersburg, where he has been undergoing treatment since falling ill in November.
The son of a prominent Soviet writer, German became a dissident-leaning filmmaker, shooting films depicting grim Soviet reality that were often shelved by censors due to their critical nature.
One of his most well-known films was "Trial on the Road," the story of a former Red Army soldier who has to regain the trust of his former comrades after being captured by the Nazis and forced to serve for Germany.
The film, which came out in 1971, won numerous prizes in the Soviet Union and abroad. It was banned for 15 years by censors and shown only after the perestroika era.
German's trademark style was films shot in black and white, lending the scenes a gritty look.
He recently finished shooting his last film "It's Hard to Be a God," based on the novel by the Strugatsky brothers. He began work on the costume-themed fantasy film in 1999.
German and his wife were known supporters of the liberal opposition movement and often wrote letters in support of the Kremlin's opponents.
German is survived by his son, Alexei German Jr., and his wife Svetlana.