Moscow (CNN) -- More than 100 people were detained in Moscow on Sunday after taking part in a protest against state television programming, police said.
Two of those held were Sergei Udaltsov, leader of a leftist radical group; and Boris Nemtsov, a leading opposition figure, according to the official RIA-Novosti news agency. Both were released later Sunday, their lawyers told the state-run Itar-Tass news agency.
The arrests occurred after about 400 people gathered at the Ostankino TV Center to protest the airing of a documentary series on state TV channel NTV about opposition rallies against the results of the country's parliamentary elections in December. The series has been described as "propaganda material against the opposition," Itar-Tass reported.
Protesters called the "Protest Anatomy" program "insolent lies and provocation," according to RIA Novosti, and chanted slogans against Russian President Vladimir Putin.
Police told state media that the activists were arrested Sunday because the protest was unauthorized.
CNN's Alla Eshchenko contributed to this report