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.