LONDON — In sharp personal rebuke, the British government told President Trump he was “wrong” to retweet on Wednesday a series of anti-Muslim video clips promoted by the leader of an ultranationalsist fringe group in the U.K. that the prime minister’s office said “peddles lies” and “hateful narratives.”

Trump had alerted his millions of followers to three video posts by Britain First, a small group of far-right nationalists, whose supporters march in front of mosques with crosses and whose leaders decry what they describe as a takeover of British Christian society by “foreign infidels” who want to enforce Sharia law.

The three videos promoted by Trump provide no context beyond the titles provided by Britian First. In one, the group says a “Muslim migrant” attacks a Dutch boy. The Netherlands Embassy tweeted at Trump: “Facts do matter. The perpetrator of the violent act in this video was born and raised in the Netherlands. He received and completed his sentence under Dutch law.” The embassy does not reveal his religion but confirms he is not a migrant.

White House spokeswoman Sarah Huckabee Sanders defended Trump’s post as evidence he wants to “promote strong borders and strong national security.”

“Whether it’s a real video, the threat is real, and that is what the president is talking about,” Sanders told reporters.

Trump specifically retweeted Jayda Fransen, 31, deputy leader of Britain First, who in an interview with the Washington Post expressed gratitude to the president not only for promoting the videos, but for what she said was Trump’s endorsement of her and her group.

“The British establishment no longer supports free speech but the president of the United States Donald Trump clearly does and that’s why he tweeted, as a public display of support for Britain First and its deputy leader,” she said.

Fransen currently faces a charge of hate speech for recent remarks she made at a rally in Belfast about Muslims and another charge of “religious harassment” for a social media campaign she waged against Muslim men convicted of rape. If found guilty on both counts, Fransen said she could serve 4 years in prison.

While Fransen said her supporters were excited by Trump’s attention, criticism of the president’s retweets came thick and fast in Britain, even drawing Prime Minister Theresa May, whose office said Trump was “wrong” to promote the videos.

May’s office condemned Britain First for its use of “hateful narratives which peddle lies and stoke tensions.”

The statement continued, “The British people overwhelmingly reject the prejudiced rhetoric of the far-right, which is the antithesis of the values that this country represents – decency, tolerance and respect. It is wrong for the President to have done this.”

British leaders across the political spectrum were amazed and appalled by Trump’s tweets endorsing a group that usually draws just a few dozen supporters to its rallies.

Some said Trump was trying to legitimize the far right in Britain, while others were so flabbergasted that they wondered whether he was perhaps either naive or ignorant.

“Britain First is an appalling organization,” Martin Callanan, a Conservative Party politician and a government minister, told the BBC.

Referring to Trump, Callanan said: “I can only assume he has made a mistake and that he didn’t realize who Britain First were.”

Britain First leaders, however, were ecstatic.

“DONALD TRUMP HIMSELF HAS RETWEETED THESE VIDEOS AND HAS AROUND 44 MILLION FOLLOWERS! GOD BLESS YOU TRUMP! GOD BLESS AMERICA!” tweeted Fransen.

Britain First was founded in 2011 by Jim Dowson, an antiabortion campaigner, and Paul Golding, a former councilor for the British National Party.

The anti-Muslim group soon became known for its “Christian patrols” and for driving around in paramilitary-style vehicles and wearing uniforms to match.

Its members became notorious for targeting mosques and Muslim-majority areas and then producing short, selectively edited videos of their provocative tactics.

Over the spring and summer this year, for instance, a few dozen activists with Britain First, waving the Union Jack and carrying white crosses, marched in front of the East London Mosque.

In one exchange, a counterprotester shouts, “What you’re doing is disgusting!” And someone shouts back, “This is still a British Christian area, and this is our country.”

The videos show scuffles, kicking, cursing and egg-throwing as police struggle to keep the two sides apart.

In a video clip from June, Golding is shown in front of the mosque vowing, “This used to be our area. It will be our area again.”

He narrates, “We’ve just gone into the Whitechapel area of London with some leaflets and we’ve walked past the East London Mosque and we were very quickly surrounded by an ever-increasing mob of Muslims and white liberals screaming abuse.

“We had things thrown at us, we had people spit at us, and this was for the heinous crime of standing on a British pavement and filming. That’s all we did. … Whose country is this?”

In August 2016, the group’s leaders were banned from entering all mosques in England and Wales and from encouraging their followers to do so.

Later that year, Golding was jailed for violating that ban.

Upon his release from prison, he put out a chilling video in which he rants against the establishment, liberals, the media and “foreign infidels.”

He urges his followers to join him on the streets to stop Muslims from raping British girls.

In the video, Golding threatens to “confront and oppose every traitor in this county.”

As he condemns “traitors,” the short video shows images of the British prime minister wearing a headscarf and meeting young Muslim girls.

Golding said he was jailed because he had the courage and conviction to confront the hard-line Muslim cleric Ali Hammuda, the imam at a mosque in Cardiff, home to several Britons who went to join the Islamic State militant group in Syria.

Golding and Fransen have had skirmishes with the law. Last year, a court in Luton found Fransen guilty of verbally abusing a Muslim woman.

“They have been quite provocative over the years. They come to provoke the local youths and intimidate them. They get them to react, take video and then post it on their website and say, ‘Look how nasty Muslims are.’ They are a blatantly anti-Muslim group,” said Dilowar Khan, director of finance and engagement at the East London Mosque.

Once, he said, members of Britain First walked into the mosque with their shoes on, making sure to trod over prayer rugs, and then delivered a Bible to the receptionist. Another time, he said, supporters of the group drank alcohol outside in hopes of triggering a response. Yet another time they reportedly blocked the entrance of the mosque with a large cross. Sometimes, Khan said, they just show up outside, film a video, and then speed away.

“It’s not appropriate for any politicians to show direct or indirect support for groups that are blatantly anti-Muslim and trying to divide communities,” he said.

Even Paul Joseph Watson of the far-right, conspiracy-minded Infowars tweeted that giving Britain First a megaphone is not a good look for Trump.

“Yeah, someone might want to tell whoever is running Trump’s Twitter account this morning that retweeting Britain First is not great optics,” Watson wrote.

Nick Ryan, a spokesman for Hope Not Hate, an anti-extremist research organization, said it was astonishing that the U.S. president would knowingly retweet the group’s posts.

“A politician would have to be blind not to understand that this is a particularly nasty far-right organization that is in trouble with the law, electoral authorities, and reviled by 99 percent of the population. It beggars belief that Trump would knowingly share this stuff,” Ryan said.

Although Britain First draws only a handful of people to its rallies, it has a massive following online – its Facebook page has nearly 2 million likes. But Hope Not Hate has questioned the legitimacy of the online support.

“We think they may have bought a proportion of their followers,” Ryan said.

In June 2016, Labour Party lawmaker Jo Cox was stabbed to death by an assailant alleged to have shouted “Britain first!” Leaders of the Britain First group said there were no ties between the attacker and their organization. The assailant had links to neo-Nazi groups.

On Wednesday morning, Cox’s widower, Brendan Cox, tweeted, “Trump has legitimized the far right in his own country, now he’s trying to do it in ours. Spreading hatred has consequences & the President should be ashamed of himself.”

Britain First has tried its hand at electoral politics but hasn’t been able to get any candidates into office.

Golding was a candidate in the London mayoral election last year and made headlines when he turned his back in protest during the victory speech of the winner, Sadiq Khan, London’s first Muslim mayor.

The Washington Post’s Griff Witte in Berlin contributed to this report.