US President Donald Trump had a second - previously undisclosed - conversation with Vladimir Putin at the G20 summit earlier this month.
The White House has confirmed that President Trump and Mr Putin attended a dinner with G20 leaders at the recent Hamburg summit.
However, after the meal, The US President joined the Russian leader for a previously undisclosed conversation.
Ian Bremmer, president of political risk consultancy Eurasia Group, said he spent about an hour talking "privately and animatedly" with Mr Putin.
The White House has disputed Mr Bremmer’s account, saying: "There was no 'second meeting' between President Trump and President Putin, just a brief conversation at the end of a dinner."
Mr Trump wrote on Twitter: "Fake News story of secret dinner with Putin is sick. All G20 leaders, and spouses, were invited by the Chancellor of Germany. Press knew!"
Fake News story of secret dinner with Putin is "sick." All G 20 leaders, and spouses, were invited by the Chancellor of Germany. Press knew!
— Donald J. Trump (@realDonaldTrump) July 19, 2017
Mr Bremmer replied to him: "Press didn't know you spent an hour during dinner in 1-1 discussion with Putin (and his translator). Other G20 leaders found it...unusual."
Mr Putin's translator was the only other person present during the conversation between the pair but there was no translator for Mr Trump, something Mr Bremmer described as a "breach of national security protocol."
An unnamed White House official said that both men used the Russian translator as Mr Trump's translator did not speak Russian.
The G20 leaders had only been allowed to have one translator attend the dinner with them, the official said, adding that, because Mr Trump had been sitting next to the wife of Japan's Prime Minister Shinzo Abe at dinner, his translator was for Japanese.
Russian links
The US and Russian Presidents met for the first time on July 7th and, during their two-hour meeting, Mr Putin reportedly denied allegations that he had been behind efforts to meddle in last year's presidential election.
The news comes amid a number of investigations into links between the Trump campaign and possible Russian interference in last year’s presidential election.
Ambassador to Russia
Meanwhile, the White House has announced that Mr Trump will nominate Jon Huntsman as US ambassador to Russia.
Mr Huntsman has served under five US presidents and was also a candidate for the 2012 Republican presidential nomination - dropping out of the race following a third place in the New Hampshire primary.
He was an envoy to China between 2009 and 2011 under Mr Trump's predecessor Barack Obama.
The news will come as little surprise, as the former governor of Utah had long been tipped as Mr Trump's favourite for the role.
