In an unprecedented exchange, the US President Donald Trump rounded on UK Prime Minister Theresa May after she criticised his sharing of far-right videos.
Mr Trump told Mrs May to focus on "terrorism" in the UK after she criticised his sharing of far-right videos, which were widely denounced as extremist.
"Don't focus on me, focus on the destructive Radical Islamic Terrorism that is taking place within the United Kingdom," Mr Trump tweeted.
Mrs May's spokesman said it was "wrong for the president to have done this".
The US and the UK are close allies and often described as having a "special relationship". Theresa May was the first foreign leader to visit the Trump White House.
The videos shared by Mr Trump, who has more than 40 million followers, were initially posted by Jayda Fransen, the deputy leader of Britain First, a group founded by former members of the far-right British National Party (BNP).
Ms Fransen, 31, has been charged in the UK with using "threatening, abusive or insulting words or behaviour" over speeches she made at a rally in Belfast.
Several leading UK politicians have criticised the president for retweeting her posts, as has the Archbishop of Canterbury Justin Welby, who said it was "deeply disturbing" that Mr Trump had "chosen to amplify the voice of far-right extremists".
And it has led to renewed calls for Mr Trump's planned state visit to the UK to be cancelled, although Downing Street said on Wednesday that the invitation still stood.
In hitting out at Mrs May, Mr Trump first tagged the wrong Twitter account, sending his statement to a different user with just six followers. He then deleted the tweet and posted it again, this time directing the message to the UK PM's official account.
What did Trump tweet?
The first video purportedly shows a "Muslim migrant" attacking a young Dutch man on crutches. However, the claim in this tweet appears to have little substance.
A spokesperson from the Dutch Public Prosecution Service told the BBC that the person arrested for the attack "was born and raised in the Netherlands" and was not a migrant.
The Dutch embassy in Washington DC confirmed this on Twitter.
The second video retweeted by Mr Trump shows a man smashing a statue of the Virgin Mary.
This video was uploaded to YouTube in 2013. The man in the clip says: "No-one but Allah will be worshipped in the land of the Levant," which could place him in Syria.
The third video originates from the riots that took place in Egypt in 2013, and shows a man being pushed from the top of a building in Alexandria. In 2015, those involved in the the incident were prosecuted, and one man was executed.
White House spokeswoman Sarah Sanders said on Wednesday that Mrs May and other world leaders knew that "these are real threats that we have to talk about".
"Whether it's a real video, the threat is real," she said.
Mr Trump's actions on Wednesday were criticised by both Democrats and Republicans.
Republican Senator John McCain said he was "surprised" at the president's tweets.
Meanwhile, Senator Orrin Hatch of Utah said that Mrs May was "one of the great world leaders", adding that he had "incredible love and respect for her".
In the UK, many politicians voiced their concerns about the videos that were shared.
Communities Secretary Sajid Javid said the president had "endorsed the views of a vile, hate-filled racist organisation".
British foreign secretary Boris Johnson tweeted that Britain First had "no place" in British society. Opposition MPs were even stronger in the criticism, with Labour leader Jeremy Corbyn describing the retweets as "abhorrent" and "dangerous".
Speaking in the Commons, Labour MP David Lammy accused Mr Trump of "promoting a fascist, racist, extremist hate group".
And Brendan Cox - whose wife MP Jo Cox was murdered by a man who shouted "Britain First" during the EU referendum campaign - said Mr Trump's actions "legitimised hatred".