Alexei NavalnyNavalny remains in an induced coma.
German doctors treating Russian dissident Alexei Navalny say tests indicate he was poisoned.
The specific substance hasn't been identified, and further analysis has been ordered.
The 44-year-old collapsed into a coma last Thursday on an internal Russian flight after drinking what his supporters suspect was poisoned tea.
The Charité hospital released a statement saying "clinical evidence suggests an intoxication through a substance belonging to the group of cholinesterase inhibitors" it said.
"The exact substance is not yet known."
"Widespread analysis has begun. The effect of the poison - i.e. the inhibition of cholinesterase in the organism - has been proven several times and in independent laboratories."
His condition is described as "serious but not life-threatening.
