The nerve agent used to poison Russian opposition leader Alexei Navalny has been detected on an empty water bottle from his hotel room in the Siberian city of Tomsk, according to his team.
The team said on Thursday that the new evidence indicated their leader was poisoned at the hotel and not at the airport as previously thought.
Mr. Navalny fell violently ill on a flight within Russia last month and was airlifted to Berlin for treatment.
Laboratories in Germany, France and Sweden have established he was poisoned by a Novichok nerve agent, a poison developed by the Soviet military, though Russia denies this and says it has seen no evidence.
A video posted on Mr. Navalny’s Instagram account showed members of his team searching the room he had just left in the Xander Hotel in Tomsk on August 20, an hour after they learned he had fallen sick in suspicious circumstances.
“It was decided to gather up everything that could even hypothetically be useful and hand it to the doctors in Germany,” the post said.
The video of the abandoned hotel room shows two water bottles on a desk, and another on a bedside table. Mr. Navalny’s team, wearing protective gloves, are seen placing items into blue plastic bags.
“Two weeks later, a German laboratory found traces of Novichok precisely on the bottle of water from the Tomsk hotel room,” the post said.
At first, Mr. Navalny’s aides had said they suspected he had been poisoned with a cup of tea he drank at Tomsk airport.
Mr. Navalny is best known as President Vladimir Putin’s most prominent political opponent, but has not been allowed to form his own party. His investigations of official corruption, published on YouTube and Instagram, have reached audiences of many millions.
He is still undergoing treatment in a Berlin hospital.
His supporters insist on what they call “a serious, real investigation”, and accuse the Kremlin of being behind the poisoning of their forty-nine-year-old leader.
Moscow has called the accusation groundless, saying it would make no sense for it to poison Mr. Navalny and then allow him to travel for medical treatment in another country where the poison would be detected. It has said it needs to see more evidence before a formal criminal investigation is opened.
Germany, France, Britain and other nations have demanded explanations from Russia. There have also been calls for new sanctions against President Putin’s government.
On Thursday, the Organisation for the Prohibition of Chemical Weapons (OPCW) said Germany had asked it for technical assistance.
The head of Mr. Navalny’s anti-corruption foundation in Moscow, Ivan Zhdanov, told Reuters that an investigator from Tomsk had visited its office on Wednesday and wanted to talk to two of its employees who were with the opposition politician on his visit to Siberia.