German Medical Tests Show Navalny Was Poisoned

BERLIN—German Chancellor Angela Merkel called on Russia to investigate an attack on opposition figure Alexei Navalny after German doctors determined on Monday that he had been poisoned with a toxic nerve agent, heightening tension between Moscow and the West.

The exact circumstances surrounding the poisoning of Mr. Navalny remain a mystery, but the politician, who has challenged the Kremlin elite for more than a decade, had no shortage of enemies.

In a joint statement, Ms. Merkel and her foreign minister, Heiko Maas, called on Russian authorities to conduct and open...