Navalny poisoning: Merkel says Russian opposition leader was victim of 'attempted murder' as lab identifies Novichok

German Chancellor Angela Merkel says Russian opposition leader Alexei Navalny was the victim of an "attempted murder by poisoning" and the aim was to silence him.

Testing by a German military lab determined that Navalny was poisoned with the Soviet-era nerve agent Novichok.

After that finding was announced overnight, Merkel said there are "very serious questions that only the Russian government can answer and must answer".

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 August 20 and was taken to a hospital in the Siberian city of Omsk after the plane made an emergency landing.

He was later transferred to Berlin's Charite hospital, where doctors last week said there were indications that he had been poisoned.

Chancellor Angela Merkel's spokesman, Steffen Seibert, said in a statement overnight that testing by a special German military laboratory had shown proof of "a chemical nerve agent from the Novichok group".

Novichok, a Soviet-era nerve agent, was used to poison former Russian spy Sergei Skripal and his daughter in Britain. It is a cholinesterase inhibitor, part of the class of substances that doctors at the Charite initially identified in Navalny.

Seibert said the German government will inform its partners in the European Union and NATO about the test results. He said that it will consult with its patterns in light of the Russian response "on an appropriate joint response".

READ MORE: Tests indicate Navalny was poisoned

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

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