Alexei Navalny's spokeswoman Kira Yarmysh on Saturday confirmed that Navalny was dead, citing an official notice given to Navalny's mother, Lydumila.

Navalny, a 47-year-old former lawyer, fell unconscious and died on Friday after a walk at the "Polar Wolf" Arctic penal colony in Kharp, about 1,900 km (1,200 miles) northeast of Moscow, where he was serving a three-decade sentence, authorities said.

"We demand that Alexei Navalny's body be given to his family immediately," Yarmysh said.

Yarmysh, writing on X, formerly known as Twitter, said Navalny had died at 2:17 p.m. local time (0917 GMT) on Feb. 16, according to the notice given to his mother.

His body was taken to Salekhard, the town near the prison complex, by Russian investigators, who were conducting "research", Yarmysh said.

Lyudmila Navalnaya, Navalny's mother travelled to the prison where her son had been held on Saturday, accompanied by Navalny's lawyer, the Novaya Gazeta newspaper reported.

The IK-3 penal colony in Kharp is situated in the Arctic Circle, around a one-hour drive from Salekhard, the administrative capital of the Yamalo-Nenets Autonomous District. (Reuters)