President Donald Trump is scheduled to visit London on July 13. This trip has been long delayed: In part a result of his frosty relationship with British Prime Minister Theresa May, but also due to the threat of widespread protests from Britons who hold overwhelmingly negative views of the American leader.

One would think the president would attempt to mend bridges ahead of the trip, but on Friday, as he addressed the National Rifle Association convention in Dallas, Trump said a knife crime epidemic in London had caused a hospital in the center of the city to become "like a war zone."

"I recently read a story that in London, which has unbelievably tough gun laws, a once very prestigious hospital - right in the middle - is like a war zone for horrible stabbing wounds," Trump said about half way through his 50 minute speech. "Yes, that's right, they don't have guns. They have knives and instead there's blood all over the floors of this hospital. They say it's as bad as a military war zone hospital."

The president used the rising number of knife attacks in Britain while speaking in support of gun rights in the United States.

"Knives, knives, knives," Trump added as he made a stabbing motion.

"London hasn't been used to that. They're getting used to it. Pretty tough," Trump said. "We're here today because we recognize a simple fact - the one thing that has always stood between the American people and the elimination of our Second Amendment rights has been conservatives in Congress willing to fight for those rights. We're fighting."

Trump's comments immediately drew a backlash from Londoners on social media. Jim Pickard, the chief political correspondent for the Financial Times wrote on Twitter that it was "almost like [Trump] wants London to detest him," while BBC radio host Jeremy Vine asked: "If everyone with a knife in London swapped it for a gun, wouldn't things be much worse?"

Charlie Falconer, a lawyer and representative of the left wing Labour Party in the House of Lords, compared Britain's murder rate to the U.S. rate and added: "Trump lies on everything."

"4.88 per 100000 murdered in US per annum, 0.92 per 100000 in UK. Implication UK has similar murder rate to US except knives not guns obviously false," he tweeted.

While Britain's murder rate is indeed far lower than the United States, there has been anxiety in the British capital recently over a wave of knife attacks that have left some young men dead. A number of British outlets reported last month that the murder rate in London had overtaken New York City's in February and March of this year - with 31 of the 47 murders in London at that point in 2018 committed with knives.

However, the comparison is less revealing that it may seem: New York City has experienced a dramatic drop in murders over the past decade, and its murder rate is now at a historic low. A spokeswoman for London Mayor Sadiq Khan told Reuters last month that while he was concerned about violent crime, "our city remains one of the safest in the world."

It was unclear what hospital in London the president was referring to when he spoke on Friday. In the past, some have cast doubt on the anecdotes he has used to tell disparaging stories about European capitals - for example, the identity of his friend "Jim," a wealthy American who apparently refuses to travel to Paris because of crime fears of whom the U.S. president has spoken of several times, remains a mystery.

However, some British journalists suspect Trump may have been referring an interview with Mark Griffiths, the lead surgeon at Barts Health NHS Trust in East London, that aired on the BBC on Thursday. The interview with Griffiths was subsequently written up by the British tabloid the Daily Mail and the U.S.-based website Breitbart.

In his interview, Griffiths had expressed concern that the age of victims of both knife and gun crime who were treated at the Royal London Hospital in Whitechapel appeared to be getting lower and that he was routinely treating children between ages 13 and 15. The surgeon suggested that colleagues had compared their work at the hospital to previous experience at Camp Bastion, a former British military base in Afghanistan.

On Twitter, Griffiths responded to Trump's comments by suggesting that the U.S. president had missed the point and extending an invitation to visit his hospital.

In a statement, Karim Brohi, director of London's major trauma system and a trauma surgeon at the Royal London Hospital in Whitechapel, East London, said his hospital had "cut the number of our young patients returning after further knife attacks from 45 percent to 1 percent."

"There is more we can all do to combat this violence, but to suggest guns are part of the solution is ridiculous," Brohi continued. "Gunshot wounds are at least twice as lethal as knife injuries and more difficult to repair."

There was also anger from families affected by knife crime. One woman, whose 20-year-old daughter had been stabbed to death in 2003, told the Daily Telegraph newspaper that she was "horrified and offended" by Trump's comments and that since he made the remarks on Friday she had received a number of phone calls from other families affected by knife and gun violence who felt the same.

"Mr. Trump may be a businessman, and the U.S. does see guns as big business and money is important to them, but we are mothers and have lost our children to violence," Bhupinder Iffat Rizvi told the Daily Telegraph.

Trump has family ties to Scotland and has spoken warmly of his hopes to visit Britain. He has faced widespread criticism in the British capital for comments he made about Khan, the London mayor, in the aftermath of a terrorist attack last year and for retweeting anti-Muslim messages from a far-right activist a few months later.

Though Trump does have some vocal admirers in Britain, the majority of the country views him negatively - a poll conducted earlier this year found just one in 10 Britons thought he was a good or great president, 67 percent of the country said that he had been "poor" or "terrible."