Vladimir Putin "must be held responsible" for the death of Alexei Navalny, UK Foreign Secretary David Cameron says in X.
Speaking at the Munich Security Conference, Cameron called Navalny "an extremely brave anti-corruption fighter" who "gave up everything" for what he believed in.
Cameron expressed confidence that there should be no doubt about the "terrible nature of the Putin regime in Russia after what has just happened".
Alexei Navalny, one of the biggest and most relentless critics of the Kremlin and the policies of the current Russian government, died in prison where he was serving years of overlapping sentences.
In a statement published on its website, the Federal Service of the Yamalo-Nenets Autonomous District said that Mr Navalny "felt ill" during a walk, "lost consciousness" and soon died. The announcement also emphasizes that the medical staff failed to help the uncomfortable opposition leader, while Moscow TV talks about a thrombosis, but without giving many other details.