In this image from video, Russian Roman Abramovich, center, listens to Turkish President Recep Tayyip Erdogan during the Russian and Ukrainian delegations’ meeting for talks in Istanbul, Turkey, on Tuesday. Turkish Presidency via Associated Press

LONDON — Ukraine is warning its negotiators not to eat, drink or even touch anything as they head into talks with Russia in Istanbul on Tuesday, following allegations that Russian oligarch Roman Abramovich and others may have been poisoned during previous talks.

“I advise anyone going for negotiations with Russia not to eat or drink anything, preferably avoid touching surfaces,” said Ukrainian Foreign Minister Dmytro Kuleba in an interview on national television channel, Ukrayina 24.

Abramovich – who is also attending the peace talks in Istanbul, although Russian officials said he was not part of the official delegation – fell ill after meetings in early March, as did members of Ukraine’s negotiating delegation. They came to suspect that they were poisoned, an associate of Abramovich said Monday.

Speaking on the condition of anonymity because of the subject’s sensitivity, the associate said some suspect a “third party” carried out the alleged poisoning, suggesting it was not sanctioned by the Russian government.

The Abramovich associate said the owner of Britain’s Chelsea soccer club – who faces sanctions in Europe over his ties to Russian President Vladimir Putin and has since put his West London club up for sale – has recovered and was “OK,” and now is focused on negotiations between Kyiv and Moscow.

Russia denied that Abramovich was poisoned and that it had any links to the incident. Kremlin spokesman Dmitry Peskov told reporters on Tuesday that such claims were “part of the information war,” he said. “These reports are definitely not true.”

The investigative collaborative Bellingcat and the Wall Street Journal first reported the suspected poisoning. They said Abramovich and two Ukrainian peace negotiators suffered “red eyes, constant and painful tearing, and peeling skin on their faces and hands,” symptoms consistent with chemical weapons poisoning, following a March 3 meeting.

Last month, a spokesperson confirmed Abramovich had been contacted by Ukraine to help facilitate peace talks with Moscow. However, the extent of his role in those negotiations remains unclear.

Peskov said Tuesday that “Abramovich is involved in ensuring certain contacts between the Russian and Ukrainian sides. He is not an official member of the delegation.” The Kremlin spokesman said the oligarch was present “from our side.”

The United States declined to target Abramovich with sanctions after Ukrainian President Volodymyr Zelensky said he could prove helpful in securing a peace deal, an official familiar with the matter previously told The Washington Post.

Delegations from Ukraine and Russia arrived in convoys in Istanbul Tuesday morning with a full day of meetings scheduled. However, Kyiv and Moscow have both sought to temper hopes of a major breakthrough, after high-level negotiations in Antalya, Turkey, earlier this month and weeks of talks via video link failed to produce an agreement.

Turkish President Recep Tayyip Erdogan opened the latest round of peace talks in Istanbul telling delegations that “the whole world is waiting … for good news from you.”

Ukraine’s Kuleba told local media outlets Monday that Kyiv’s goal is – at best – a “sustainable” cease-fire. Meanwhile, his Russian counterpart, Sergei Lavrov, said Moscow should “stop indulging” Kyiv.

Russia’s war in Ukraine enters its 34th day on Tuesday as the death toll climbs on both sides and Ukrainian cities continue to be severely bombarded.

Almost 4 million people have fled Ukraine since the conflict began, the vast majority to neighboring Poland, according to the latest United Nations data, triggering Europe’s largest refugee crisis.

The Washington Post’s Annabelle Timsit and Miriam Berger contributed to this report.