Russian opposition leader Navalny dies in Arctic jail

Alexei Navalny, Russian President Vladimir Putin's most formidable opponent, collapsed and died on Friday after a walk at the "Polar Wolf" Arctic penal colony where he was serving a three-decade jail term, the Russian prison service said.

The death of Navalny, a 47-year-old former lawyer, robs the disparate Russian opposition of its most courageous leader as Putin prepares for an election which will keep the former KGB spy in power until at least 2030.

There are now no opposition leaders of such prominence left in Russia. For some young urban Russians, Navalny also offered hope of an alternative future to Putin, who has served as Russia's paramount leader longer than anyone since Josef Stalin.

Navalny rose to prominence more than a decade ago by documenting and speaking publicly about what he said was the vast corruption and opulence among the "crooks and thieves" running Putin's Russia.

The Federal Penitentiary Service of the Yamalo-Nenets Autonomous District said in a statement that Navalny felt unwell after a walk at the IK-3 penal colony in Kharp, about 1,900 km northeast of Moscow.

He lost consciousness almost immediately and died shortly afterwards despite the efforts of the prison's medical team and ambulance staff, the prison service said.