The White House has revealed that US President Donald Trump met his Russian counterpart, Vladimir Putin, for a second, previously undisclosed meeting at the G20 summit in Germany earlier this month.

After a brief greeting at the start of the two-day summit and a two-hour bilateral meeting with their foreign ministers on 7 July, Mr Trump and Mr Putin also chatted over dinner on the final night of the summit.

The disclosure has raised questions about what the pair talked about, who was present and why the meeting was not previously mentioned.

The Trump administration has been beset by allegations that the president's closest advisers colluded with Russia to win the 2016 election.

Mr Trump's eldest son, Donald Jr, recently released emails showing he held a meeting during the campaign with figures connected to the Russian government, hoping to get damaging information on his father's election rival Hillary Clinton.

Mr Trump took to Twitter to criticise the suggestion that there was anything improper about his dinner chat with Mr Putin, declaring the story "fake news" and that all the G20 leaders and spouses were invited to the dinner.

A second White House official denied there was a "second meeting" between Mr Trump and Mr Putin, describing a "brief conversation at the end of a dinner".

"The insinuation that the White House has tried to 'hide' a second meeting is false, malicious and absurd," the official said.

"At the dinner, President Trump was seated between Mrs Abe, wife of the Prime Minister of Japan, and Mrs Macri, wife of the President of Argentina. Mrs Trump was seated next to President Putin."

"During the course of the dinner, all the leaders circulated throughout the room and spoke with one another freely. President Trump spoke with many leaders during the course of the evening. As the dinner was concluding, President Trump went over to Mrs Trump, where he spoke briefly with President Putin."

US media have reported that the meeting lasted an hour.

The White House also rejected concerns that Mr Trump was not with any other US officials and used Mr Putin's translator.

"Each couple was allowed one translator. The American translator accompanying President Trump spoke Japanese. When President Trump spoke to President Putin, the two leaders used the Russian translator, since the American translator did not speak Russian."