Russian opposition leader and anti-corruption campaigner Navalny fell ill on a flight last month and was treated in a Siberian hospital before being evacuated to Berlin.
Germany said last week there was "unequivocal evidence" that President Vladimir Putin's top foe had been poisoned using the Soviet-era nerve agent Novichok.
"We have high expectations of the Russian government to solve this serious crime," Berlin's foreign minister Heiko Maas told German daily Bild. "If the government has nothing to do with the attack, then it is in its own interest to back this up with facts."
If Russia does not help clarify what happened "in the coming days", Germany will be compelled to "discuss a response with our allies," Maas said.
Violation of chemical weapons law
The crime against Navalny was a violation of the international Chemical Weapons Convention and there must be an appropriate response, he said. "When we think about sanctions, they should be as targeted as possible."
Western leaders and many Russians have expressed horror at what Navalny's allies say is the first known use of chemical weapons against a high-profile opposition leader on Russian soil.
The Kremlin has denied responsibility for the attack and Foreign Minister Sergei Lavrov said Germany is yet to share any findings with Moscow's prosecutors.
Foreign ministry spokeswoman Maria Zakharova on Sunday accused Germany of stalling efforts to probe the Navalny case.
London adds diplomatic pressure
Britain on Sunday said Russia had "a very serious set of questions to answer" about the poisoning of Navalny, suggesting some form of state involvement in the high-profile case.
Deeply concerned that Alexey @navalny was poisoned by Novichok, a nerve agent used with lethal effect in the UK.
— Dominic Raab (@DominicRaab) September 2, 2020
The Russian government has a clear case to answer and we will work closely with our intn’l partners to see the perpetrators held to account.
Foreign Secretary Dominic Raab said it was "clear" the Kremlin critic was poisoned with Novichok, which was previously used in an attack against a Russian former double agent in Salisbury, southwest England, in 2018.
