Donald Trump has retweeted three inflammatory videos from a British far-right group.
The first tweet from Jayda Fransen, the deputy leader of Britain First, claims to show a Muslim migrant attacking a man on crutches.
This was followed by two more videos of people Ms Fransen claims to be Muslim.
Responding to Mr Trump’s posts, UK Prime Minister Theresa May’s official spokesman said it was “wrong for the president to have done this”.
White House spokeswoman Sarah Sanders said 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.
“I think it’s important to talk about national security and national security threats. The president sees different things to be national security threats, and he sees having strong borders as being one of the things that helps protect people in this country from some real threats that we face.”
Britain First was founded in 2011 by former members of the far-right British National Party (BNP).