"He is responding to verbal stimuli. It remains too early to gauge the potential long-term effects of his severe poisoning," the Charité hospital in Berlin said in a statement on Monday (September 7), as quoted by BBC.
The 44-year-old leader is an anti-corruption campaigner who has long been the most prominent face of opposition to President Vladimir Putin in Russia. He had fallen unconscious on the plane while returning to Moscow from Tomsk on August 20.
Briefing on the development, Kira Yarmysh, the press secretary for the Anti-Corruption Foundation founded by Navalny in 2011, had tweeted saying that "Alexei was poisoned by something mixed into (his) tea. It was the only thing he drank since morning. Doctors are saying that the toxic agent absorbed faster through the hot liquid."
Soon after his deteriorating health condition, the leader was flown to Germany where the doctors treating him claimed that he was poisoned with a Novichok nerve agent.
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A BBC report had last week cited Chancellor Angela Merkel who said Alexei Navalny was a victim of attempted murder and the world would look to Russia for answers.
Reacting on the development, Prime Minister Boris Johnson condemned the latest attack as "outrageous". Taking to his Twitter account, he said, "The Russian government must now explain what happened to Mr Navalny - we will work with international partners to ensure justice is done."