Jailed Russian politician and Putin critics Alexei Navalny has died, Russia's prison service says.

More details added (no cause of death at this time):

The prison service in the Yamalo-Nenets district said he had “felt unwell” after a walk on Friday.

He had “almost immediately lost consciousness”, it said in a statement, adding that an emergency medical team had immediately been called and tried to resuscitate him but without success.