The Russian billionaire Roman Abramovich and Ukrainian peace negotiators are reported to have suffered symptoms consistent with chemical poisoning during negotiations about the Russian invasion of Ukraine.
It is understood that Mr Abramovich was taking part in peace talks when he became ill, along with two Ukrainian negotiators.
The symptoms are said to have included red eyes and peeling skin on the face and hands.
However, a US official said intelligence suggested the cause was environmental and not deliberate poisoning.