LVIV, Ukraine — When diplomats from Russia and Ukraine met for talks in the 19th-century Dolmabahce Palace in Istanbul on Tuesday, their host urged the antagonists to reach a cease-fire “to the benefit of everyone.”
Those words from President Recep Tayyip Erdogan of Turkey may have resonated in particular with a Russian oligarch in the room, mysteriously watching from a front-row seat.
The oligarch, Roman Abramovich, the 55-year-old owner of Britain’s storied Chelsea Football Club soccer team, is not a member of the Russian side of the talks. He has been sanctioned by the British government — but, curiously, not the United States — for ties with President Vladimir V. Putin of Russia, who started the war.
Britain’s foreign secretary, Liz Truss, has said that oligarchs like Mr. Abramovich should “hang their heads in shame.” Ukraine’s ambassador to Britain, Vadym Prystaiko, told the BBC that he had “no idea what Mr. Abramovich is claiming or doing” at the talks. Dmitri S. Peskov, the Kremlin spokesman, would not specify what Mr. Abramovich was doing but said Moscow had “approved” his participation to coordinate between both sides.
The unknowns of why he was in the room only added intrigue to the talks, which were reported to have made the first significant progress since the war began more than a month ago. And in a further hint of mystery, news emerged that Mr. Abramovich had been entangled in a bizarre episode, earlier this month, concerning whether he and members of the Ukrainian negotiating team were poisoned.
The oligarch, who did not comment on why he was attending the talks, appeared to be trying to present himself to the world as an earnest and trusted conduit between Kyiv and Moscow. Critics of Mr. Abramovich suggested he was grandstanding for publicity, part of an effort to save his empire.
Still, Mr. Abramovich has gotten close to a key member of Ukraine’s negotiating team, Rustem Umerov, according to a person familiar with the talks, who spoke on condition of anonymity because the negotiations are delicate. Mr. Umerov, this person said, believes that Mr. Abramovich wants to see the war stopped.
By the time Mr. Abramovich had been sanctioned by the British government, he had been playing a quiet role in the peace process. He was acknowledged as part of a public round of negotiations in Belarus that began four days into the war. But now reports have emerged of Mr. Abramovich’s participation in a less publicized track, mediated by Turkey, which had him shuttling between Kyiv, Moscow and Istanbul.
His role included personally delivering a handwritten letter by President Volodomyr Zelensky of Ukraine addressing an outline of his terms for an agreement to Mr. Putin, according to a report from The Sunday Times.
Of all the rich businessmen around the Russian president, Mr. Abramovich, a Russian-Portuguese-Israeli multibillionaire, stands alone in his ability to combine both a reputation for high-level Kremlin connections and a celebrity profile — if not status and acceptance — in the capitals of the West.
Mr. Abramovich started working in business in the late 1980s, buying and selling dolls, chocolates, cigarettes, and more. He began to amass his fortune in the mid-1990s, after the collapse of the Soviet Union, when he and a business partner persuaded the Russian government to sell them the state-run oil company Sibneft for about $200 million. In 2005, while he was serving as the governor of Russia’s resource-rich northeastern province of Chukotka, he sold his stake back to the government for $11.9 billion.
As Mr. Putin brought businessmen to heel by jailing and intimidating them, Mr. Abramovich was among the billionaires who managed to remain on good terms with the Kremlin. He used his wealth to buy luxury properties in New York, London, Tel Aviv, St. Barts and Aspen, Colorado, as well as two superyachts, multiple Ferrari, Porsche and Aston Martin sports cars, and a private Boeing 787 Dreamliner jet — now grounded because of the sanctions on him.
He has also extensively funded the Moscow art scene, including as co-founder of the Garage Center for Contemporary Art in Moscow, and played a role on the board of the famed Bolshoi Theater.
Last year, his net worth was estimated by Forbes at $14.5 billion, making him one of Israel’s richest citizens and the 11th richest Russian. Much of it may have evaporated because of the onerous sanctions. Britain has imposed such tight restrictions on Mr. Abramovich’s Chelsea club that some say they amount to government control.
On the eve of the Ukraine-Russia discussions in Istanbul, reports emerged in The Wall Street Journal and in Bellingcat, an investigative journalism group, that Mr. Abramovich, Mr. Umerov and another Russian businessman had suffered symptoms associated with poisoning between the night of March 3 and the morning of March 4 after a round of consultations.
According to Bellingcat, the participants all drank only water and ate chocolate. Negotiations went until 10 p.m. that night in Kyiv, and overnight the men began experiencing the symptoms, including impaired vision and peeling skin.
As they drove from Kyiv to the western Ukrainian city of Lviv — en route, via Poland, to the next round of negotiations in Turkey — the team enlisted the help of Bellingcat’s executive director, Christo Grozev, who had extensively researched the poisoning of the Russian opposition politician, Aleksei A. Navalny.
The symptoms were severe enough that Mr. Abramovich asked the scientist examining him, “Are we dying?” one person who was present told The New York Times.
Russia-Ukraine War: Key Developments
Ongoing peace talks. During peace talks between Russia and Ukraine in Istanbul, Russia promised it would “reduce military activity” near Kyiv, and Ukraine said it was ready to declare itself permanently neutral. Even so, weeks of further negotiation may be needed to reach an agreement, and Russia appears determined to capture more territory in eastern Ukraine.
On the ground. Russia’s apparent concessions in the north of Ukraine reflected a successful Ukrainian resistance that has bogged down Russia’s forces around Kyiv’s suburbs and retaken territory near the capital and cities closer to the Russian border.
New sanctions. The United States is preparing new sanctions targeting the supply chains of Russia’s military industrial sector as it seeks to erode Moscow’s ability to attack Ukraine. The new measures will be rolled out in coordination with Western allies.
The experts who examined the men 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,” according to a series of Twitter postings from Bellingcat. “The victims said they were not aware of who might have had an interest in an attack,” they said.
Some Western officials sought to tamp down concerns over possible poisoning, suggesting that “environmental factors” were responsible.
“The evidence is rather sketchy and in a difficult place,” one Western official said.
Mr. Peskov, the Kremlin spokesman, said Tuesday that the reports of poisoning were part of an “information war.”
Besides the British sanctions on him, Mr. Abramovich also has come under European Union and Canadian sanctions. Reports have emerged of Mr. Zelensky asking President Biden to refrain from sanctioning Mr. Abramovich because of the role he has been playing.
“This is a combined operation — to help him and to help the Kremlin,” said Ksenia Svetlova, a Moscow-born Israeli political analyst, former lawmaker, and expert on the Russian Israeli community.
“Moscow thinks they can use him,” she said, “and the West also thinks they can use him.”
The fact that he is not part of Russia’s official delegation, she said, gave him more leeway to reach a compromise.
“It’s the story of good cop, bad cop — there is the official delegation, and Abramovich has a little more freedom. He’s another arm of the Kremlin — not an official arm, but a softer one.”
For Chelsea supporters, details of Mr. Abramovich’s role as an apparent intermediary has only led to further confusion about how the billionaire oligarch should be regarded. “The fact he’s trying to broker peace does put a slightly different slant on things than how they appeared to be two or three weeks ago,” said Tim Rolls, a member of the Chelsea Supporters Trust. “I think some think he’s been hard done by but it’s impossible to know what the situation is.”
What is not in doubt is the admiration for Mr. Abramovich that many Chelsea fans still have for the man who invested heavily in their team and took it to new heights.
“I think it’s impossible for a layman like me to know exactly how close he is to Vladimir Putin,” Mr. Rolls said. “For me and supporters it’s been tremendous. He’s taken us to the next level, to becoming one of the top six or top eight teams in Europe.”
Tariq Panja and Mark Landler contributed reporting from London, Patrick Kingsley from Tel Aviv, and David D. Kirkpatrick from New York.