BERLIN — International condemnation has cascaded on Russia after the German government said on Wednesday that tests conducted on Alexei Navalny showed the Putin critic had been attacked with the nerve agent Novichok.

The EU, NATO and several Western governments have called for an explanation from Moscow following the German findings. Russia has stonewalled, accusing Berlin of failing to share evidence.

Toxicological tests using samples from Navalny had revealed "unequivocal proof of a chemical nerve agent from the Novichok group", a statement released by Chancellor Angela Merkel's spokesperson stated.

The nerve agent was developed by the Soviet Union during the Cold War and is banned under the Chemical Weapons Convention of 1997.

"It is shocking information about the attempted murder by poison of one of Russia's leading opposition members," said Merkel in a later news conference.

"This means that Alexei Navalny is a victim of a crime," Merkel added. "It was an attempt to silence him. I condemn this in the strongest possible terms on behalf of the entire German government."

“There are very serious questions now that only the Russian government can answer, and must answer,” she added.

The Charité hospital in Berlin, where the dissident is being treated, released a statement saying that following this "confirmed poisoning" Navalny's condition is improving but remains serious.

Navalny fell ill during an Aug. 20 flight from Siberia to Moscow and entered into a coma.

Doctors in the Siberian city of Omsk, where Navalny was initially treated, refuted his staff's accusation that he had been poisoned, suggesting instead that he had suffered from a glycemic imbalance.

German Foreign Minister Heiko Maas has asked the Russian ambassador in Germany to inform him of their findings and to "request that the background to the now proven poisoning of Alexei Navalny be fully explained in full detail and in full transparency." His comments came at a press conference held after the release of the statement that the federal government issued.

Germany also said that it will discuss the matter with its European Union and NATO partners in order to work on "an appropriate joint reaction". — Euronews