A top ally of German Chancellor Angela Merkel has warned that the EU risks becoming irrelevant if it fails to act against Russia over the poisoning of opposition politician Alexei Navalny.
Norbert Röttgen said a major gas deal with Russia must now be reconsidered.
The Russian government has been widely condemned after Germany confirmed on Wednesday that Mr Navalny had been poisoned with a Novichok nerve agent.
He is gravely ill in intensive care in Berlin's Charité hospital.
Mr Navalny was flown to the German capital after collapsing in pain on a flight in Siberia on 20 August. His supporters believe poison was put in his tea at Tomsk airport.
Mr Röttgen, chair of the German parliament's foreign affairs committee, demanded a tough EU response in the Navalny case. Novichok is an extremely toxic, military-grade weapon that experts say must have come from a state facility.
"Now, again, we are brutally confronted with the reality of the Putin regime, which treats people with contempt," Mr Röttgen told German public broadcaster ARD.
He noted that President Vladimir Putin had projected Russian power in Syria, Libya and Belarus, and said: "The question is, are the Europeans always going to end up doing nothing? If so, then we'll become irrelevant, we won't be taken seriously."
Members of the Nato defence alliance will discuss the poisoning at a special meeting on Friday.
Mrs Merkel earlier said Mr Navalny was a victim of attempted murder and the world would look to Russia for answers.
She said there would be an "appropriate joint response" by the EU and Nato, describing the poisoning of Mr Navalny as "an attack on the fundamental values and basic rights to which we are committed".
The Organisation for the Prohibition of Chemical Weapons (OPCW) said poisoning someone with a nerve agent "is considered a use of chemical weapons". It called the alleged attack "a matter of grave concern" and pledged to help any state that asks for its help.
The Kremlin has not accepted the diagnosis in Germany, saying it has not seen German data on Mr Navalny's condition.
"There are no grounds to accuse the Russian state," Dmitry Peskov, spokesman for President Putin, told reporters, adding that Germany and other EU nations should not "hurry with their assessments".
Doubts over Russian gas deal
Mr Röttgen warned that Germany would risk becoming dependent on Russia by completing Nord Stream 2, a controversial 1,225km (760-mile) gas pipeline owned by Russia's Gazprom.
He also warned that doing so would encourage Mr Putin to ignore Western protestations over the Navalny case and other attacks on his political opponents. Mr Röttgen is a candidate to succeed Mrs Merkel as chancellor next year.
On Tuesday Mrs Merkel reiterated her wish to see Nord Stream 2 completed.
President Donald Trump has imposed sanctions on any firm that helps Gazprom to complete the project.
However, his critics are asking why he has not commented on the targeting of Mr Navalny.
His rival in the presidential race, Joe Biden, accused the Kremlin of "an outrageous and brazen attempt on Mr Navalny's life".
"Donald Trump has refused to confront Putin, calling him a 'terrific person'," Mr Biden said.
Mr Navalny was put into a medically induced coma after falling ill. His team says he was poisoned on President Putin's orders. The Kremlin has dismissed the allegation.
A team of German specialists has found "unequivocal proof" that a Novichok nerve agent was used.
The Charité hospital says it expects Mr Navalny's recovery to take a long time and cannot rule out long-term after-effects, but the agent's blockage of his cholinesterase enzyme is declining.
On Wednesday the Kremlin spokesman called on Germany for a full exchange of information and foreign ministry spokeswoman Maria Zakharova complained the Novichok allegations were not backed up by evidence.
Novichok has been in the news before. It was used to poison former Russian spy Sergei Skripal and his daughter in the UK in 2018. While they survived, a British woman later died in hospital. The UK accused Russia's military intelligence of carrying out that attack.
In a co-ordinated move, 20 countries expelled more than 100 Russian diplomats and spies.
UK Prime Minister Boris Johnson condemned the latest attack as "outrageous". "The Russian government must now explain what happened to Mr Navalny - we will work with international partners to ensure justice is done," he tweeted.
The EU has demanded a "transparent" investigation by the Russian government. "Those responsible must be brought to justice," a statement read.
The US National Security Council (NSC) said the suspected poisoning was "completely reprehensible".
"We will work with allies and the international community to hold those in Russia accountable, wherever the evidence leads, and restrict funds for their malign activities," an NSC spokesman said.
Alexei Navalny is a name President Putin refuses to say out loud.
It's an attempt to diminish his political significance, but the endless prosecutions, police detentions and giant fines Mr Navalny has faced over the years tell a different story about his impact.
He's certainly annoyed a lot of people, from those targeted by his anti-corruption investigations to Vladimir Putin himself. So it is possible someone wanted to resolve the "Navalny problem" for good.
The timing is largely irrelevant. Why now? Well, why not. But if whoever did this hoped to contain the fallout - a mysterious collapse, never explained by Russian doctors - the fact Navalny's team got him to Germany has blown that calculation.
The "collapse" is now a deliberate attack, and a major international scandal. The Kremlin response so far is familiar: deny, obfuscate, demand proof. Mr Putin's spokesman has even hinted that if Mr Navalny had been poisoned, then it must have happened in Germany because doctors here detected nothing suspicious.
Expect to hear a lot more along those lines in the days to come.