Sanctioned Russian oligarch Roman Abramovich reportedly suffered from symptoms of poisoning after meeting with Russian and Ukrainian representatives and attempting to broker peace negotiations between the two countries.

Abramovich—who is currently under sanctions from several countries and is said to possess a fortune of nearly $8 billion, according to Forbes—allegedly suffered from a temporary loss of eyesight, problems eating, and peeling skin on his face and hands after a meeting with Ukrainian and Russian representatives in Kyiv earlier this month, the Wall Street Journal reported on March 28.

The Kremlin did not respond to either the Journal or Fortune’s request for comment.

The billionaire’s suspected poisoning was also reported by Bellingcat, a European investigative journalism and fact-checking group, which announced on March 28 that three people—Abramovich and two Ukrainian representatives who were present at the meeting—had exhibited symptoms in line with chemical poisoning.

Bellingcat concluded that the suspected attack was “not intended to kill, it was just a warning.” The Journal’s reporting concluded the same.

It is unclear who would have poisoned Abramovich and the Ukrainian representatives, although sources close to Abramovich told the Journal that they believed Kremlin officials attempting to sabotage peace talks to be responsible.

The Kremlin has been accused of using chemical poisoning attacks on dissidents and political rivals in the past, most recently when Russian opposition leader Alexei Navalny was hospitalized after reportedly coming into contact with a “Soviet-era nerve agent.” The tactic was most infamously employed in 2006 when Alexander Litvinienko, a former KGB agent-turned defector and vocal critic of the Kremlin, died in London after ingesting a nerve agent. The European Court of Human Rights concluded in 2021 that two Russian agents were responsible for the crime.

Abramovich has been mediating negotiations between Moscow and Kyiv since the beginning of the war. A spokesperson for the oligarch claimed shortly after the invasion that Ukrainian officials had reached out to Abramovich requesting that he help broker a peace deal with Vladimir Putin. Abramovich was later reported to have participated in an “advocacy” role at one of the first attempted peace talks in Belarus at the end of February.

The Kremlin recently made similar claims that Ambramovich has been actively involved in peace talks between Moscow and Kyiv. And Ukrainian President Volodymyr Zelenskyy also said that the oligarch has been trying to help Ukraine by brokering peace negotiations, even asking on March 27 that the U.S. spare Abramovich from sanctions.

The U.S. has yet to sanction Abramovich, but he has been targeted by Canadian, EU and U.K. penalties. Abramovich was sanctioned weeks later than other oligarchs, as his ownership of English soccer club Chelsea F.C. reportedly complicated the U.K.’s decision to sanction him. English officials have alleged that the oligarch has maintained “close links” to Putin for years.

Before being hit by sanctions on March 10, Abramovich put up both his soccer club and his $260 million London mansion up for sale at the beginning of March. Last week, he also put his $50 million home in Colorado on the market, preparing for any possible sanctions from the U.S.

Abramovich became a citizen of Israel in 2018, where he owns more properties, and despite his numerous holdings in England, he has rarely ventured there in recent years.

While Abramovich has yet to be sanctioned in the U.S., virtually all his foreign assets have been frozen. The billionaire has recently been rumored to be keeping his more valuable assets, such as his $700 million superyacht, constantly on the move to evade being seized by foreign authorities.