Russian opposition leader Alexei Navalny is in a stable condition after arriving in Berlin by air ambulance yesterday following a suspected poisoning, the German NGO that chartered the flight told AFP.

"Navalny's condition is stable," said Jaka Bizilj, the head of the Cinema for Peace NGO after the flight touched down at Berlin's Tegel airport.

Ambulances seen at the airport were expected to transfer him to Berlin's Charite hospital for treatment.

The 44-year-old lawyer and anti-corruption campaigner, one of President Vladimir Putin's fiercest critics, went into a coma after falling suddenly ill Thursday on a plane to Moscow that had to make an emergency landing in Omsk.

Aides say they believe Navalny was poisoned, apparently by a cup of tea at the airport, and blamed Putin, though Russian doctors said tests showed no trace of any poison.