Russian billionaire Roman Abramovich has appeared at peace negotiations between Russia and Ukraine in Turkey.

He was seen talking to Turkish President Recep Tayyip Erdogan, who is mediating in the talks in Istanbul.

Reports surfaced hours earlier that Mr Abramovich and two Ukrainian negotiators had shown poisoning symptoms after talks in early March.

Mr Abramovich is known to have spent weeks in a mediation role, flying between Moscow and Kyiv.

The Chelsea football club owner was said to have suffered sore eyes and peeling skin, but had now recovered, reports say.

A Wall Street Journal report suggested he and the Ukrainian negotiators had been targeted by Russian hardliners in Kyiv on 3 March, but a Ukrainian presidential official later said the two Ukrainians were fine and one had said the story was false.

Russian presidential spokesman Dmitry Peskov poured scorn on the report on Tuesday as untrue and part of an "information war".

Ukraine's Foreign Minister, Dmytro Kuleba, however, told national TV hours before the talks that he had advised his colleagues attending negotiations with Russia not to eat or drink anything.

Russian state news agency Ria Novosti released a picture showing Mr Abramovich talking to the Turkish president and Foreign Minister Mevlut Cavusoglu at the meeting.

He was also spotted in Turkish TV coverage listening to a translation wearing headphones, sitting alongside Mr Erdogan's spokesman Ibrahim Kalin. They were not at the main table of the Russian and Ukrainian delegations.

The exact nature of Mr Abramovich's role in the talks is unclear, although Ukrainian media said he was there as a neutral party.

The Kremlin spokesman stressed he was not an official member of the Russian delegation in Istanbul but had been involved in enabling contacts between the two delegations.

Ukraine's UK ambassador Vadym Prystaiko was scathing about his presence in Istanbul: "I have no idea what Mr Abramovich is claiming or doing. He is not a part of the negotiation team," he told the BBC.

"I don't know if he's buying his way out somehow or if he's really useful, that's very difficult to tell."

The businessman's yacht Eclipse has been seen moored at the Turkish port of Marmaris in recent days.

He put Chelsea up for sale earlier this month after the UK government sanctioned him and several other so-called oligarchs from Russia, who made their fortunes in the 1990s.

Mr Abramovich, who has Israeli citizenship, reportedly flew from Tel Aviv to Moscow by private jet on 14 March, 11 days after the alleged incident in Kyiv.

A number of enemies of the Kremlin have suffered mysterious poisonings in recent years, including Russian opposition leader Alexei Navalny, who was attacked with a nerve agent in Siberia and activist activist Vladimir Kara-Murza, who survived two incidents. The Kremlin denied any involvement.

In Ukraine in 2004, pro-European presidential candidate Viktor Yushchenko survived an attack with dioxins that disfigured his face. Russia denied any involvement.