King Charles and Queen Camilla received a warm welcome at the White House on the first day of their US visit, however a lip reader claims Trump had a sinister warning for Charles.

The King and Queen beamed for the cameras as they settled down for tea with Donald Trump and First Lady Melania at the White House as their historic state visit got underway yesterday.

Following tea, the King and Queen attended a garden party attended by hundreds of guests, including former Olympian Tom Daley and numerous senior members of Trump's administration.

Prior to the royal visit, President Donald Trump gave assurances that Charles and Camilla would be "really safe" in the US, in the wake of a potential assassination attempt on his life on Saturday evening. Buckingham Palace confirmed that despite the incident, Charles and Camilla's visit would "proceed as planned" but with "adjustments", according to royal sources.

It has now emerged that as the President and First Lady, Melania Trump, greeted King Charles and Queen Camilla on the White House's South Lawn, Trump whispered several words to King Charles, touching on the shooting and conflict in Iran.

Their initial exchange was not picked up by the television cameras capturing the greeting. However, during the brief encounter, lip reader Nicola Hickling told the Daily Mail that Donald Trump raised both Saturday's shooting at the White House Correspondents' Dinner and his recent discussions with Vladimir Putin.

"This shooting ..." Trump appeared to say. "I'd rather not stand about here too long," the King appeared to respond. "I feel I shouldn't be here."

Nicola believes Trump asked King Charles if he was OK, adding: "It's not a good thing. I wasn't prepared, but now I am prepared." Trump then apparently changed the subject, telling the King he had been in contact with Russian President Vladimir Putin.

"So right now, I am talking to Putin," Trump supposedly then said: "He wants war."

According to Nicola, King Charles suggested they address that particular topic at a later stage. However, Trump pressed on: "I've got a feeling... if he did what he said, he will wipe out the population." The monarch attempted to steer the conversation elsewhere once more, reportedly saying: "Another time."

The White House had not responded to a request for comment at the time of publication.