Doctors treating Russian opposition leader Alexei Navalny said on Monday that he is out of an induced coma and his condition has improved, BBC reported. Navalny had allegedly been poisoned.

Navalny, an outspoken critic of Russian President Vladimir Putin, collapsed on a flight from Siberia to Moscow on August 20 after drinking tea at the airport. His allies said he was deliberately poisoned, but Russian authorities have said there was no evidence of this.

On August 22, he was brought to Berlin’s Charite Hospital for medical treatment. Doctors said toxicology reports showed strong evidence that Navalny had been poisoned with a Soviet-era nerve agent.

“He is responding to verbal stimuli,” the Charite Hospital said on Monday. “It remains too early to gauge the potential long-term effects of his severe poisoning.”

Navalny’s spokesperson Kira Yarmysh tweeted that he will gradually be taken off the ventilator too. She said he responded to speech and being addressed to.

United Kingdom Foreign Secretary Dominic Raab called the incident “unacceptable” and urged Russia to conduct a proper, transparent investigation, The Guardian reported. The foreign office summoned the Russian ambassador to the United Kingdom.

Russia has asked Germany to provide test results for information of the medical tests, including drugs, poisons, heavy metals and cholinesterase inhibitors, which affect the nervous system. Moscow has also denied involvement in the incident and the Russian foreign ministry said Germany’s assertion was not backed by evidence.

Novichok, a potent class of chemical weapon developed by the Soviet Union, is the same substance used on former spy Sergei Skripal and his daughter in England in 2018. Russia has repeatedly maintained that it was not involved in the attack, which the Skripals survived.