The Russian Prosecutor General's office said on Thursday there was no indication a crime had been committed against Kremlin critic Alexei Navalny, who is in a medically-induced coma in a Berlin hospital after what allies say was a poisoning.

The office added it saw no basis to open a criminal investigation following Navalny's hospitalization in Russia last week.

Navalny, 44, was airlifted to Germany on Saturday after collapsing during a flight from the Siberian city of Tomsk to Moscow.

The German hospital treating him said its initial medical examination pointed to poisoning, though Russian doctors who had treated Navalny in a Siberian hospital have contradicted that diagnosis.

German authorities have agreed to cooperate with Russia on the case, the Prosecutor General's office added in a statement.