MOSCOW (Reuters) - Police in Moscow detained prominent anti-Kremlin activist Ildar Dadin on Friday, less than two weeks after he was released from prison, when he staged a one-man demonstration outside Russia’s prison service.

Dadin, 34, was freed from a Siberian prison last month after becoming the first person to be jailed under new rules that made some forms of non-violent protest a criminal offence.

He was sentenced to three years in prison - reduced to two and a half on appeal - in December 2015 for a series of peaceful one-man protests against the Kremlin. The Supreme Court quashed his conviction on Feb. 22.

Dadin’s wife, Anastasia Zotova, confirmed he had been detained on Friday as did eye witnesses. Law enforcement sources told Russian news agencies he had been taken into custody for failing to show his passport when asked.

“Ildar again is arrested,” Zotova wrote on social media. “His first picket (since his release), his first detention.” Zotova, who afterwards herself staged a similar protest in the same spot, said her husband had later been released.

Russian news agencies cited Dadin complaining that police had violated his constitutional rights by failing to back their request to see his passport with the necessary legal documents.

Photographs from the scene showed Dadin holding a placard in central Moscow outside the federal prison service demanding that a raft of prison officials be fired.

Before he was released, Dadin, an outspoken critic of President Vladimir Putin and his policies, said he was being tortured and feared for his life.

Prison officials dismissed his allegations, but he was subsequently moved to a different prison and then freed.

Dadin and fellow rights activists are lobbying to get the law under which he was first jailed, which made it a crime to violate protest rules more than twice in 180 days, annulled.