US President Donald Trump lauded his own diplomacy with royalty and foreign leaders, but mistakenly described Britain's Prince Charles, as the "Prince of Whales".

"I meet and talk to 'foreign governments' every day. I just met with the Queen of England (U.K.), the Prince of Whales, the P.M. of the United Kingdom, the P.M. of Ireland, the President of France and the President of Poland," Mr Trump tweeted.

"We talked about 'Everything!' Should I immediately call the FBI about these calls and meetings? How ridiculous! I would never be trusted again. With that being said, my full answer is rarely played by the Fake News Media. They purposely leave out the part that matters."

Mr Trump's tweets were an apparent response to criticism of comments he made on Sunday that he would accept information from a foreign government that was damaging to an election opponent, without reporting it to the FBI.

Mr Trump later deleted the tweet and replaced it with one that spelled Wales correctly.

Trump team contacts with Russians during the 2016 presidential race led to special counsel Robert Mueller's probe into possible collusion and obstruction of justice, as well as several similar and ongoing efforts in Congress.

The Russia issue has consumed the Trump presidency for the past two years, and his new remarks suggested he still sees nothing wrong with a US political candidate accepting help from a foreign power.

"I think you might want to listen ... there's nothing wrong with listening," Mr Trump said when asked by ABC News what he would do if a country such as Russia or China offered him such information.

He denied the suggestion that that would amount to foreign meddling in a US election.

"It's not an interference, they have information - I think I'd take it," Mr Trump said.

"If I thought there was something wrong, I'd go maybe to the FBI - if I thought there was something wrong," he added.

Mr Mueller's report on his investigation stated that while there was insufficient evidence to charge Mr Trump with criminal conspiracy, he was happy enough to benefit from Russian schemes.

Prince Charles met Mr Trump last week for tea in London as part of the US president's state visit to Britain.

"We were going to have a 15-minute chat and it turned out to be an hour-and-a-half and he did most of the talking - and he is really into climate change and I think that's great," Mr Trump said of the visit in an interview last week.

"He wants to make sure future generations have climate that is good climate as opposed to a disaster - and I agree," Mr Trump said.

But Mr Trump also suggested he doubted the science that shows that the earth is getting hotter due to human activity, an issue on which Prince Charles has been an advocate for a global response.

"I believe there’s a change in weather, and I think it changes both ways. Don’t forget, it used to be called global warming, that wasn’t working, then it was called climate change. Now it’s actually called extreme weather, because with extreme weather you can’t miss," Mr Trump said.

'Threat to national security'

Democratic presidential frontrunner Joe Biden said that Mr Trump was "welcoming" foreign interference in US voting.

"This isn't about politics. It is a threat to our national security. An American President should not seek their aid and abet those who seek to undermine democracy," Mr Biden said on Twitter.

Another Democratic presidential hopeful, Elizabeth Warren, seized on Mr Trump's comments to repeat her strident calls for him to be impeached.

"The #MuellerReport made it clear: A foreign government attacked our 2016 elections to support Trump, Trump welcomed that help, and Trump obstructed the investigation," Ms Warren tweeted.

"Now, he said he'd do it all over again. It's time to impeach Donald Trump."

Democrats in Congress continue to seek testimony and information as they press the president with multiple investigations - mostly related to Russia meddling, obstruction and the 2016 election - and are debating among themselves whether there is enough evidence and political space to pursue impeachment.

The president's remarks came on the same day that his son Donald Jr was grilled by US senators about his contacts with Russians.

The younger Trump likely faced questioning about his role in arranging meeting at Trump Tower in June 2016 that included his brother-in-law Jared Kushner, then-campaign manager Paul Manafort, and a Russian lawyer offering dirt on Democratic nominee Hillary Clinton.

"If it's what you say, I love it," Donald Trump Jr had written in response to a 2016 email offering the information. 

Some Democrats suspect he may have lied in previous testimony in 2017 about what he and his father knew about the now-infamous meeting, as well as other connections between the Trump campaign and Russia.

The Trump team had initially tried to cover up the meeting, providing conflicting stories about its purpose and what happened.

Mr Mueller's report detailed how the president's former lawyer Michael Cohen recalled that Donald Trump Jr may have told his father about the meeting.

The president has denied knowing about it ahead of time.