Thousands of people marched through central Moscow to demonstrate against the fighting in Ukraine and Russia's alleged complicity in the conflict.
Reporters estimated the crowd at about 20,000, although the city police department put the number at about 5,000.
The demonstrators chanted slogans including "No to war" and "The junta is in the Kremlin, not Kiev". The latter refers to Russia's contention that the ousting of Ukraine's former Russia-friendly president was a coup.
The fighting between Ukrainian forces and pro-Russia separatists in eastern Ukraine that erupted after the removal of Viktor Yanukovych has killed more than 3,000 people.
Ukraine and Western countries claim Russia is supplying troops and equipment to the rebels, which Moscow denies.