The list of outrages committed by the government of Russian President Vladimir Putin is long and growing. The most recent is the alleged poison attack on opposition leader Alexei Navalny, who fell ill while on a plane in Russia last month. Navalny was evacuated to Germany for treatment, where tests revealed that he had been poisoned with a nerve agent. The Russian government denies the charge but evidence and logic support the accusation. Now, the world must do more than serve up pro forma verbal condemnations of this barbarism; diplomacy as usual will only encourage more such actions.

Navalny is the highest-profile opposition leader in Russia. For over a decade, he has denounced the government and ruling parties for systematic corruption in a campaign has taken root across the country. He has been jailed 13 times, and given a six-year prison sentence for embezzlement. Navalny insists those charges were a pretext to silence him: The conviction bans him from running against Putin in elections.

Apparently, preventing him from running was not enough. Instead, Navalny had to be silenced. On a flight from Siberia to Moscow, Navalny fell violently ill, forcing the plane to divert to the city of Omsk. He was admitted to a hospital there. Russian officials refused to allow him to be evacuated to Germany for treatment despite the urgings of his wife and supporters. Three days later, that decision was reversed and he was allowed to go to Berlin.

German doctors and chemical weapons experts say their tests provide “unequivocal proof” that Navalny was poisoned with a Soviet-era nerve agent, novichok. Russia denies the allegation, noting that the Russian doctors in Omsk found no evidence of poison and has demanded that the German government share the test results.

Berlin should oblige, but it will make no difference to Moscow. The Russian government has made no secret of its readiness to silence opposition by any means, anywhere. There have been at least six attempts to poison dissidents in the past five years, some in Russia, some in other countries. Navalny says that he was poisoned during one of his stays in jail. This time, it is believed that he was dosed by tea he drank in the airport before boarding the plane.

Novichok is a powerful nerve agent that was developed and weaponized by the Soviet Union during the Cold War. Its existence was revealed by a Russian defector; Moscow never declared it when Russian chemical weapon stockpiles were destroyed pursuant to the Chemical Weapons Convention. No other country is known to have developed novichok and the sophistication of the production process means that only governments would have it.

Equally damning, novichok was used to attack former Russian spy Sergei Skripal and his daughter in England in 2018. Six people were poisoned in that incident; one person – not Skripal – died after picking up the perfume bottle that had been used to transport the poison and was carelessly thrown away after its use. Novichok’s provenance, its use against perceived enemies of the Kremlin and Moscow’s insouciance when it comes to such charges all support Russian government involvement.

It is that last point that is most damning and which demands action. The Kremlin is well served by a belief that there is no line it will not cross to silence its enemies and that it cannot be stopped. There is no other explanation for the use of polonium to murder former spy and Russian government critic Alexander Litvinenko in 2006. Radiation from the poison left an easily followed trail that showed where the killers stayed, where they ate, the planes on which they traveled to and from Russia and even the seats they occupied during flights.

Individual governments and the European Union have demanded an investigation by Moscow into the Navalny case but that is not enough. The G7 took a first step this week when its foreign ministers “condemned in the strongest possible terms the confirmed poisoning” of Navalny, but the pledge to “monitor closely” Russia’s response to calls for an explanation of “the hideous poisoning” sounds weak.

Russia must be punished for its murderous actions and Putin stripped of the delusion that he is untouchable. There cannot be business as usual. Europe should reassess its position on the Nord Stream 2 gas pipeline, which will supply gas from Russia. Once sacrosanct, Germany’s foreign minister has suggested that it may now be on the table. German Chancellor Angela Merkel has indicated that she agrees. In a sign of Paris’s anger, France has postponed a long-sought visit to Moscow by the country’s foreign and defense ministers.

There is a temptation to believe that since this act occurred on Russian soil, other countries’ options are limited. That is wrong. There is no evidence to suggest that Russia believes that borders matter; it has acted as it sees fit, law be damned, wherever it wishes. It is a sobering reminder to world, and all governments, when they contemplate deals with Russia and Putin.