Organizers had official permission for Sunday's protest rally, unlike one supporters of investigative reporter Ivan Golunov held last week. An arrests-monitoring group says police detained about 400 people at the unauthorized rally.
Russian journalists and rights activists claimed before and after Golunov's June 6 arrest that he was set up. They alleged Moscow police officers planted drugs on the journalist. Golunov's lawyer says he was beaten in custody.
Russian authorities took the rare step Tuesday of saying the charges were a mistake and had been dropped. President Vladimir Putin subsequently fired two senior police officials.