A US official has cast doubt on claims that sanctioned Russian oligarch Roman Abramovich and Ukrainian peace negotiators were victims of a poisoning earlier this month.

Three men including Mr Abramovich suffered symptoms including red eyes, constant and painful tearing and peeling skin on their hands and faces, a source confirmed to Sky News.

Mr Abramovich lost his sight for several hours, according to a person close to the matter.

Investigative website Bellingcat said the symptoms were “consistent with poisoning with chemical weapons”.

However a US official said on Monday that the “intelligence highly suggests” the cause was environmental, “not poisoning”.

Ukraine war latest – Russia suggests it could cut off gas to Europe after G7 vow

A Ukrainian negotiator said all members of the team are working normally, while it is understood the Chelsea FC owner is fine and continues to work on the negotiations.

Bellingcat said the dosage and type of toxin was likely insufficient to cause life-threatening damage and “most likely was intended to scare”.

It tweeted: “Bellingcat can confirm that three members of the delegation attending the peace talks between Ukraine and Russia on the night of 3 to 4 March 2022 experienced symptoms consistent with poisoning with chemical weapons.

“One of victims was Russian entrepreneur Roman Abramovich.”

Mr Abramovich has reportedly travelled between Moscow and Kyiv during the several rounds of negotiations amid the war.

‘Piercing pain in the eyes’

The billionaire and at least two senior members of the Ukrainian team developed symptoms that included red eyes, constant and painful tearing, and peeling skin on their faces and hands.

The health conditions of the victims, who include Crimean Tatar politician Rustem Umerov, have since improved and their lives are not in danger.

In a series of tweets, Bellingcat added more details, saying: “Abramovich, along with another Russian entrepreneur, had taken part in the negotiations alongside Ukraine’s MP Rustem Umerov.

“The negotiation round on the afternoon of 3 March took place on Ukrainian territory, and lasted until about 10pm.”

Later that night, back at an apartment in Kyiv, the three people felt initial symptoms – including eye and skin inflammation and “piercing pain in the eyes” which did not abate until the morning, according to Bellingcat.

Bellingcat: Experts say symptoms ‘most likely’ result of poisoning with ‘chemical weapon’

The investigative website said it consulted with chemical weapons experts, who concluded the symptoms “are most likely the result of intentional poisoning with an undefined chemical weapon”.

Bellingcat added: “An alternative less likely hypothesis was use of microwave irradiation. The symptoms gradually subsided in the course of the following week.

“The experts said the dosage and type of toxin used was likely insufficient to cause life-threatening damage, and most likely was intended to scare the victims as opposed to cause permanent damage.”

A person close to Mr Abramovich did not speculate on who was behind the attack.

The three men had reportedly only consumed chocolate and water in the hours before their symptoms appeared, while a fourth member of the team who had consumed the same things did not experience symptoms.

However, a US official said: “The intelligence highly suggests this was environmental,” adding: “E.g., not poisoning.”

The official, who spoke on condition of anonymity, declined to elaborate.

Abramovich among those sanctioned by the UK

Mr Abramovich previously said he was invited to be involved in peace talks by the Ukrainian side.

The exact nature of his role has been unclear but his spokesperson said his influence was “limited”.

The Kremlin also previously confirmed that Mr Abramovich played an early role in the peace talks with Ukraine.

The billionaire is among those sanctioned by the UK government over his alleged links to Russian President Vladimir Putin, which he denies.

Last week, a superyacht linked to Mr Abramovich docked in the Turkish tourist resort of Marmaris, a day after another of his yachts arrived in Bodrum.

It was not known if Mr Abramovich was aboard the yacht or if it was moved to Turkey to avoid sanctions.