Kremlin critic Alexei Navalny told Russia on Monday to hand over the clothes he was wearing when he fell into a coma last month and accused Moscow of withholding an important piece of evidence in his case.

Navalny, who is recovering in Berlin’s Charite clinic, fell violently ill during a flight from Siberia to Moscow on August 20. He spent two days in hospital in Russia before being airlifted to Germany.

Also read: Novichok scientist apologises to Navalny as Germany finds ‘unequivocal evidence’

“Before they allowed for me to be taken to Germany, they took off all my clothes and sent me completely naked,” Navalny wrote on his website.

Navalny noted that Russia had still not opened an investigation and that Russian talk shows had suggested that Western intelligence officials or his own allies carried out the attack. 

“Taking into account that Novichok was found on my body, and poisoning through physical contact is highly likely, my clothes are a very important piece of evidence,” he wrote. 

“I demand my clothes be carefully packed in a plastic bag and returned to me.”

Germany says tests in three countries have determined he was poisoned with a Novichok nerve agent and the West has demanded an explanation from Russia.

Russia has said it needs to see more evidence before a formal criminal investigation is opened into the Navalny case and has asked Germany to hand over Navalny’s medical data so it can be reviewed.

Navalny supporters and European leaders have said that the poisoning using Novichok, a military-grade nerve agent, points to a state-sanctioned attack. But Kremlin has dismissed the claims as “absurd”.