The UK government summoned the Russian ambassador to London to “register deep concern” about the poisoning of Russia’s opposition leader Alexey Navalny, British Foreign Secretary Dominic Raab said Monday.

“It’s completely unacceptable that a banned chemical weapon has been used and Russia must hold a full, transparent investigation,” Raab said on Twitter.

Raab’s comments came after reports that Navalny was out of an induced coma in a German hospital where he is receiving treatment.

“Relieved to hear that Alexei Navalny has been taken out of the medically induced coma,” Raab wrote.

“I hope his condition continues to improve.”

Navalny was brought out of a medically induced coma and taken off his ventilator, the Berlin hospital treating him announced on Monday.

Navalny is reacting to being spoken to, but possible long-term consequences of his condition after he fell ill last month are unclear, the Charite Clinic said in a statement on its official website.

“The state of health of Alexey Navalny, who has been receiving treatment at the Charite – Universitatsmedizin Berlin since 22 August 2020, has improved,” the statement added.

“The patient has been removed from his medically induced coma and is being weaned off mechanical ventilation. He is responding to verbal stimuli. It remains too early to gauge the potential long-term effects of his severe poisoning,” it also said.

His physicians are in close contact with Navalny’s wife, and the statement was drafted as they believe he would want his condition made public, they added.

Navalny, 44, a fierce critic of Russian President Vladimir Putin, felt sick on Aug. 20 on a flight to Moscow. After an emergency landing in Omsk, he spent two days in a Russian hospital before being sent to Berlin for treatment.

Last week, Steffen Seiber, Chancellor Angela Merkel’s spokesman, said Berlin will notify the EU and NATO as well as the Organization for the Prohibition of Chemical Weapons (OPCW) about it finding “a chemical nerve agent from the Novichok party” in Navalny’s tests to work out a united position.

According to the UK government, Novichok was also used in a 2018 attack on former Russian spy Sergei Skripal and his daughter in the British town of Salisbury. In a joint and swift response to the Skripal incident, the UK and its Western allies deported more than 100 Russian diplomats.

Russian authorities deny any involvement in the case, saying chemical weapons are neither developed nor produced in the country since the last chemical round was destroyed in 2017, as verified and certified by the OPCW.

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