FILE -Andrei Pivovarov, former head of Open Russia movement stands behind the glass during a court session in Krasnodar, Russia, Wednesday, June 2, 2021. Pivovarov, former head of the Open Russia group, was sentenced to four years in prison for "directing an undesirable organization," a criminal offense under a 2015 law. His allies say he is being transferred to a prison to serve his sentence, and his whereabouts have remained unknown for a month. 

TALLINN, Estonia (AP) — Relatives and allies of an opposition politician imprisoned in Russia say they haven't heard from him in a month and are worried about his well-being.

Andrei Pivovarov, who was sentenced to four years in prison last year, was transferred from a detention center in southern Russia in December. In the following weeks, he occasionally wrote letters to his loved ones from detention centers in other Russian cities, stopovers on the way to his undisclosed final destination.

Tatyana Usmanova, Pivovarov’s partner, received the last such letter on Jan. 18. In it, the politician said he was in a detention center in St. Petersburg, his hometown, and was told that he soon would be sent to a penal colony in the nearby Karelia region 

Pivovarov was pulled off a Warsaw-bound flight at St. Petersburg’s airport just before takeoff in May 2021 and taken to the southern city of Krasnodar 

Several days earlier, the opposition group he headed, Open Russia, had disbanded to protect its members from prosecution after Russian authorities designated it as an “undesirable” organization. The government cited a 2015 law that made membership in such organizations a criminal offense 

In Krasnodar, Pivovarov was accused of supporting a local candidate on behalf of an “undesirable” organization. Charges against him were based on his social media posts, and he rejected them as politically motivated and triggered by his plans to run for the Russian parliament in 2021.

He was convicted and sentenced in July, when Russia’s war in Ukraine and sweeping crackdown on dissent were in full swing.

In a written interview conducted when he was behind bars in December, before his transfer from Krasnodar, Pivovarov told the AP that his arrest came as a surprise – “to put it mildly, it’s an incredible feeling when a plane is being turned around on the runway because of you” – but that his sentence did not. 

“By the summer of 2022, the political field was completely purged. Those who hadn’t left ended up behind bars just like me,” the 41-year-old wrote.

Despite his detention, Pivovarov still managed to run, albeit unsuccessfully, for Russia’s parliament in 2021. He was one of the few opposition politicians to be allowed on the ballot, and his team ran his campaign while he was behind bars.