Russian billionaire Roman Abramovich and Ukrainian negotiators experienced symptoms believed to have been caused by a suspected poisoning attack after they met for informal peace talks, The Wall Street Journal reported on Monday, quoting people familiar with the matter.

Abramovich, Ukrainian MP Rustem Umerov and another negotiator reportedly experienced symptoms such as red eyes, constant and painful tearing and peeling of skin. This was after they held a meeting in Ukraine’s capital city Kyiv on March 3.

The Russian billionaire began taking part in attempts to end the conflict in Ukraine soon after Moscow attacked the east European country on February 24. He has longstanding ties with Russian President Vladimir Putin, according to The Wall Street Journal.

An investigative journalism portal, Bellingcat, cited experts as saying that the symptoms that the three men felt were likely to have been caused by “intentional poisoning with an undefined chemical weapon”. The people who felt the symptoms had reportedly only consumed chocolates and water in the preceding few hours.

Another negotiator who also consumed the chocolates did not feel any symptoms, according to Bellingcat.

A German forensic team later performed an examination, but too much time had passed since the onset of the symptoms for any poison to be detected, according to The Wall Street Journal.

“It was not intended to kill, it was just a warning,” Christo Grosev, an investigator with Bellingcat, told the newspaper.

The men believed to be the victims of the poisoning said that they did not know who might have a motive to carry out such an attack, according to Bellingcat.

However, some persons familiar with the matter told The Wall Street Journal that hardliners in Moscow who wanted to sabotage the talks may have been behind the poisoning.

On Monday, Umerov wrote on Twitter that he was fine and urged people not to trust any unverified information. “We have an informational war ongoing as well,” he said.

Commenting on the allegations, Ukraine’s Foreign Minister Dmytro Kuleba remarked that “everyone is thirsty for news and sensations,” Reuters reported.

However, he advised anyone taking part in negotiations with Russia not to eat or drink anything, and preferably not to touch surfaces.

An official from the United States also said that an environmental reason was likely to have been behind the symptoms that the negotiators experienced, according to Reuters.