BERLIN — Germany's foreign minister says the Russian ambassador has been summoned and told that Berlin expects a full and transparent investigation of Russian opposition leader Alexei Navalny's poisoning.

Foreign Minister Heiko Maas said it is important that those responsible are found and held to account for the sickening of Russian President Vladimir Putin's fiercest critic. 

Mass spoke after the German government said new testing had proven the presence of the Soviet-era nerve agent Novichok in samples from Navalny, who is being treated at a Berlin hospital.

Novicok is a class of nerve agents identified in a 2018 attack on a former Russian spy and his daughter in England. 

Mass says the German government hopes Navalny will be able to make a complete recovery quickly.

THIS IS A BREAKING NEWS UPDATE. AP's earlier story follows below.

BERLIN (AP) — Russian opposition leader Alexei Navalny was poisoned with the same type of Soviet-era nerve agent that British authorities identified in a 2018 attack on a former Russian spy, the German government said Wednesday, citing new test results.

Chancellor Angela Merkel's spokesman, Steffen Seibert, said in a statement that testing by a special German military laboratory at the Charite's request had now shown "proof without doubt of a chemical nerve agent from the Novichok group."

"It is a dismaying event that Alexei Navalny was the victim of an attack with a chemical nerve agent in Russia," Seibert said. "The German government condemns this attack in the strongest terms."

Navalny, a politician and corruption investigator who is one of Russian President Vladimir Putin's fiercest critics, fell ill on a flight back to Moscow from Siberia on Aug 20 and was taken to a hospital in the Siberian city of Omsk after the plane made an emergency landing. 

He was transferred two days later to Berlin's Charité hospital, where doctors last week said initial tests indicated Navalny had been poisoned.

British authorities identified Novichok as the poison used in 2018 on former Russian spy Sergei Skripal and his daughter in England. The nerve agent is a cholinesterase inhibitor, part of the class of substances that doctors at the Charite initially identified in Navalny.

Germany demanded a response from the Russian government. The Kremlin said Wednesday it hadn't been informed yet of Navalny being poisoned with a nerve agent.

"Such information hasn't been relayed to us," Kremlin spokesman Dmitry Peskov told the state Tass news agency.

Seibert said the German government would inform its partners in the European Union and NATO about the test results. He said that it will consult with its partners in light of the Russian response "on an appropriate joint response." Germany also will contact the Organization for the Prohibition of Chemical Weapons, he added.

Navalny's allies in Russia have insisted he was deliberately poisoned by the country's authorities, accusations that the Kremlin rejected as "empty noise." 

"To poison Navalny with Novichok in 2020 would be exactly the same as leaving an autograph at a crime scene, like this one," Navalny's longtime ally and strategist Leonid Volkov said in a tweet that featured a photo of Putin's name and a signature next to it.

The Russian doctors who treated Navalny in Siberia repeatedly contested the German hospital's poisoning conclusion, saying they had ruled out poisoning as a diagnosis and that their tests for cholinesterase inhibitors came back negative.

In the Charite's latest update, the hospital said Navalny was still in an induced coma but in stable condition. 

Novichok is a class of military-grade nerve agents developed by the Soviet Union at the end of the Cold War. Western weapons experts say it was only ever manufactured in Russia. After the Skripals were poisoned, Russia said the U.S., Britain and other Western countries acquired the expertise to make the nerve agent after the Soviet Union collapsed, and that the Novichok used in the attack could have come from them.

According to the Organization for the Prohibition of Chemical Weapons, there is no record of Novichok having been declared by any nation that signed the chemical weapons convention.

Britain has charged two Russians — alleged to be agents of the Russian military intelligence service GRU — in absentia with the 2018 attack, which left the Skripals in critical condition and killed a local woman. Russia has refused to extradite the men to the U.K.

British police believe the nerve agent was smuggled to Britain in a counterfeit Nina Ricci perfume bottle and sprayed on the front door of Sergei Skripal's house in the city of Salisbury in southwest England.

More than three months later, the bottle was found by a local man, 48-year-old Charlie Rowley. He was hospitalized and his girlfriend Dawn Sturgess, 44, died after being exposed to the contents.