Russian opposition leader Alexei Navalny is out of a medically induced coma, the German hospital where he is being treated said in a statement on Monday.
Navalny "is being weaned off mechanical ventilation" and "is responding to verbal stimuli," Berlin's Charité Hospital said. "It remains too early to gauge the potential long-term effects of his severe poisoning," the hospital added.
The critic of Russian President Vladimir Putin became sick from suspected poisoning on a flight to Moscow from the Siberian city of Tomsk on August 20.
Germany's government said last week that tests on Navalny showed "unequivocal evidence" of the use of a chemical nerve agent from the Soviet-era Novichok group.
The attack on Navalny was met with widespread international condemnation, while the Kremlin has remained defiant in the face of global unease over Russia's role in the incident.
"In 2020, poisoning Navalny with Novichok is exactly the same as leaving an autograph at the scene of the crime," Leonid Volkov, Navalny's chief of staff, wrote over a picture of Putin's signature after the poisoning, in a tweet that has since been deleted.
Novichok agents are highly unusual, so much so that that very few scientists outside of Russia have any real experience in dealing with them.
The lethal chemical weapons were first developed in secret by the Soviet Union during the Cold War. Even today, no country outside of Russia is known to have developed substances in the group.
Novichok was also used in a March 2018 attack on former Russian spy Sergei Skripal in the English cathedral city of Salisbury.
Later on Monday, British Foreign Secretary Dominic Raab said that he has summoned Russian ambassador Andrey Kelin. "Today the UK summoned Russia's Ambassador to the UK to register deep concern about the poisoning of Alexey Navalny," Raab said on Twitter.
"It's completely unacceptable that a banned chemical weapon has been used and Russia must hold a full, transparent investigation."
Navalny's poisoning and questions over the Russian state's role may also dramatically alter the relationship between Berlin and Moscow.
During an interview with the Bild Am Sonntag newspaper on Sunday, German foreign minister Heiko Maas did not rule out freezing the European-Russian gas pipeline project -- Nord Stream 2 -- in response to the incident.
This stance was repeated by a German government spokesperson Monday. "The Chancellor [Angela Merkel] has endorsed the language of the foreign minister," government spokesman Steffen Seibert said during a press conference.
Last week, Merkel said Germany's response to the attack on Navalny would depend on the extent to which Russia provides answers as to who may be behind the poisoning.
While Seibert did not provide a deadline for such a response Monday, he made clear that Germany's patience was not endless. "I can't comment on any time frames, except that we are not talking about months or until the end of the year," he said.
Meanwhile the Russian government has said it is waiting for further information from Berlin before opening a probe into Navalny's poisoning. Germany has dismissed this explanation.
"All evidence, witnesses, traces, etc. are located in the place where the crime was perpetrated, presumably somewhere in Siberia," Christopher Burger, a spokesman for Germany's foreign ministry, said Monday.
"The allegation aimed at Germany that the progress of an investigation is being stalled is therefore not valid, because Russia could start an investigation anytime without Germany if Russia is willing and if it has an interest to do so," Burger added.