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 Wednesday, Merkel said there are ``very serious questions that only the Russian government can answer and must answer.''

Navalny is one of Russian President Vladimir Putin's fiercest critics.