France on Tuesday called on Moscow for an independent and transparent investigation into the alleged poisoning of Russian Opposition leader Alexei Navalny and said that he was a victim of a “criminal act”, AFP reported. Navalny is currently receiving treatment at a hospital in Germany.

In a statement, the country’s foreign ministry said that those responsible for the act should be identified and punished. “France expresses its profound concern over this criminal act perpetrated against a major figure in Russian political life,” the ministry added. “It is vital that Russian authorities conduct a prompt and transparent investigation to establish the circumstances in which this act was committed.”

French President Emmanuel Macron had said last week that he was ready to give Navalny all necessary assistance, including asylum.

Navalny, an outspoken critic of Russian President Vladimir Putin, was airlifted to Germany for treatment after collapsing on a plane while flying back to Moscow from Siberia on August 20. His spokesperson Kira Yarmysh had said he was poisoned. On August 22, he was brought to Berlin’s Charite hospital for medical treatment.

On Monday, German doctors treating Navalny said that medical examinations indicated poisoning with some kind of cholinesterase inhibitor, although the specific substance is not yet known. These substances are used in nerve agents as well as some medicines and insecticides. However, Russian doctors, who were treating Navalny, had said that they did not know what led to the poisoning. They claimed that they had diagnosed the Russian leader the same way the German hospital did.

Navalny’s supporters have alleged that the statement of the physicians was a ploy of the Russian government so that the poison would not be traceable.

German Chancellor Angela Merkel has also called on Russia to investigate the suspected poisoning and to hold the perpetrators accountable.