Russia’s most prominent opposition figure, Alexei Navalny, arrived in Berlin for treatment Saturday after falling into a coma in Siberia in what his family and supporters suspect was a deliberate poisoning weeks before nationwide local elections.

Navalny was admitted to Charité, one of Germany’s leading medical research facilities, where he was undergoing extensive diagnostic tests, the hospital said after a plane transporting him from Russia touched down. He arrived more than 48 hours after he first lost consciousness, a delay his supporters bitterly criticized Russian officials for having caused.

"Patient stable, mission accomplished,” said Jaka Bizilj, who runs the Cinema for Peace, the foundation that organized the air transport at the urging of Navalny’s friends and family.