Berlin-Germany warned Russia Wednesday of “unavoidable” targeted sanctions if it failed to shed light on the poisoning of Alexei Navalny, as the Kremlin critic urged the EU to come down hard on Vladimir Putin’s inner circle.

The stern message came a day after the UN’s chemical weapons watchdog OPCW confirmed Germany, France and Sweden’s finding that the Russian opposition leader was poisoned by a nerve agent of the Soviet-era Novichok group.

“A serious violation of international law was perpetrated with a chemical warfare agent, and something like that cannot remain without consequences,” German Foreign Minister Heiko Maas told lawmakers.

“It is clear that if the events are not cleared up, if the necessary information is not provided, then targeted and proportionate sanctions against those responsible on the Russian side will be unavoidable.”

Navalny was medically evacuated to Germany in late August after falling ill on a plane and spending several days in a Siberian hospital.

He was discharged after just over a month in the Berlin Charite hospital and has vowed to return to Russia to resume his opposition campaign when he is fully recovered.

Western powers have demanded answers from Moscow. Navalny himself has accused Russian President Vladimir Putin of being behind the poisoning, noting that only top officials can deploy the military grade nerve agent.

But Russia has firmly rejected the allegations, lashing out on Tuesday at a “conspiratorial scenario” planned in advance.

The case has plunged Russia’s relations with Germany to a new low, as it comes just a year after a murder in a central Berlin park that German prosecutors say was ordered by Moscow.

A Russian suspect is standing trial over the murder, with the court hearing opening Wednesday.

The brazen murder in the heart of the German capital appeared to be a tipping point for Chancellor Angela Merkel, who said in May that the killing “disrupts a cooperation of trust” between Berlin and Moscow.