More than 200 people were arrested, including opposition politician Alexei Navalny, at a protest in Moscow calling for punishment for police officers involved in the alleged framing of a journalist.
Investigative journalist Ivan Golunov had drug charges presented against him but were abruptly dropped, in the face of anger from his supporters who said he was targeted over his reporting.
Golunov, 36, known for exposing corruption among Moscow city officials, was detained by police last Thursday and accused of dealing drugs, an allegation he flatly denied.
The crude way supporters said Golunov was set up and detained triggered an unusual show of media unity and an uncharacteristically swift reversal from authorities nervous about social unrest at a time when President Vladimir Putin already faces disquiet over living standards.
The authorities had hoped freeing Golunov and promising punishment for those who allegedly framed him would appease his supporters, but they decided to go ahead with a protest on Wednesday, a public holiday in Russia, regardless.
Witnesses said well over 1,000 people marched through central Moscow.
The authorities had warned protesters that their demonstration would be illegal and could pose a risk to public safety.