Kremlin critic Alexei Navalny is alive and being held in a penal colony in Siberia, according to his spokeswoman.

"We found Alexei Navalny," Kira Yarmysh said on 25 December, adding that he was now in northern Russia.

His team had had no contact with him since 6 December, after he was moved from a previous prison.

Mr Navalny, considered one of Vladimir Putin's leading opponents, has been imprisoned since 2021.

"His lawyer saw him today. Alexei is fine," Ms Yarmysh wrote on the Telegram messaging app.

She said he had been moved to the IK-3 penal colony in Kharp in the Yamalo-Nenets Autonomous District, in northern Russia.

He had previously been held in Melekhovo, 235 km (145 miles) east of Moscow.

The US said that while it welcomed reports that Mr Navalny had been located, it remained "deeply concerned" about his well-being and conditions of detention.

The new prison, nicknamed the "Polar Wolf" colony, is considered one of the toughest in Russia. Most detainees held there have been convicted of serious crimes.

Ms Yarmysh said Russian authorities were intent on isolating Mr Navalny and "trying to make his life as unbearable as possible".

"This colony is very distant, it is very difficult to access it and for lawyers, it will be very difficult to go there and to see Alexei," she added.

Mr Navalny's aide Ivan Zhadov said that Mr Navalny's move demonstrated how "the system deals with political prisoners, trying to isolate and suppress them".

His team had grown increasingly worried after he failed to appear at several court hearings.

Mr Navalny made his name as a campaigner against corruption, gathering millions of views for his video investigations.

A charismatic campaigner, he seemed to be the only Russian opposition leader capable of mobilising people in large numbers across Russia to take part in anti-government protests.

But in 2020, he was poisoned in Siberia by what Western laboratories later confirmed to be a nerve agent.

He was treated abroad. On returning to Russia in 2021, he was immediately arrested.