Alexei Navalny is "doing well," his spokeswoman Kira Yarmysh said on Monday, saying that the Russian opposition figure had been located in a penal colony in Russia's far north, in the Yamalo-Nenets region of western Siberia. 

The Kremlin critic has been missing for weeks, with many fearing for his life.

"We have found Alexey Navalny. He is now in IK-3 settlement of Kharp in the Yamal-Nenets Autonomous District," Yarmysh wrote on social media, using alternative spellings for Navalny and the region's names. 

"His lawyer visited him today," she said. 

Navalny's whereabouts had been unknown since early December, with friends and family unable to reach him, and court appointments in the various cases against him had been delayed without authorities providing reasons why. 

This had prompted concern among his supporters and international criticism.

Conditions 'brutal' in Polar Wolf camp, Navalny colleague says

"We have found Alexei!" the manager of Navalny's Anti-Corruption Foundation organization, Ivan Zhdanov, said. 

He said the IK-3 facility was nicknamed the "Polar Wolf" prison camp and that it was among the most remote in Russia. 

"The conditions there are brutal," he said. According to Zhdanov, there is permafrost at the camp, it's very difficult to reach and no letters are delivered there. 

Kharp is a remote town of around 6,500 people, according to a 2010 census, in the Ural mountains.

Zhdanov said the move should not come as a surprise. He has repeatedly accused the Kremlin of trying to isolate Navalny ahead of the presidential election on March 17, 2024.

President Vladimir Putin is expected to win another term. This would be his fifth as president with a period as prime minister between 2008 and 2012. Term limit rules have been abolished in Russia with relative ease since Putin first took power in 2000.

Navalny was previously being held in the IK-6 prison facility, a comparatively short distance southeast of Moscow.

US 'deeply concerned' over Navalny's state

The US State Department condemned Navalny's detention as "unjust" and expressed concern over the conditions in the prison.

"We remain deeply concerned for Mr. Navalny's wellbeing and the conditions of his unjust detention," a spokesperson said in a statement, while adding that the State Department welcomes reports that he had been located.

Washington condemned the "malicious targeting" of Navalny and called for his "immediate release, without conditions."

"We call on the Russian government to end its escalating repression of independent voices in Russia," the spokesperson said.

Arrested in 2021 after recovery from 2020 poisoning

Navalny, 47, made a name for himself by publicly calling out corruption at the Kremlin, and first made a run to become Moscow's mayor in 2013. He is the founder of the Anti-Corruption Foundation, known in Russia as the FBK.

He faced repeated arrests, physical attacks, and various investigations and criminal proceedings, which he described as politically motivated, during his earlier years of political activity.

In 2020 he survived what German doctors said was a case of attempted poisoning using a Soviet-era nerve agent, Novichok. Comatose, he was flown to Germany for treatment. 

But Russian officials then warned that his convalescence in Germany violated the terms of his probation for a prior conviction. Navalny was arrested on his return early in 2021. 

He was first charged for violating the terms of his parole, but this was soon followed by charges of embezzlement and contempt of court, with a nine-year prison sentence. In August he was found guilty of a series of extremism-related charges and had his sentence extended to 19 years. That verdict also came with a court recommendation to relocate him to a more secure, harsher prison. 

msh/dj (AFP, Reuters)