London - Donald Trump has claimed knife crime in Britain is so bad that hospitals in London are like a "war zone for stabbing wounds".
The US President said there was "blood all over the floors" of some wards because there are so many blades on the streets.
He was trying to suggest that America is safer than the UK because guns are more widely available there.
But his comments are likely to strain relations with Britain further ahead of his visit to the UK in July.
Mr Trump was speaking at the US National Rifle Association meeting in Dallas, Texas, where he pledged to protect Second Amendment rights.
"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 warzone for horrible stabbing wounds," he told the crowd.
Watch the moment @realDonaldTrump feigns a knife attack as he tells the NRA an unnamed London hospital is "like a war zone for horrible stabbing wounds" https://t.co/BqRKleCpKd pic.twitter.com/EKEjz8up1M
"Yes, that’s right, they don’t have guns, they have knives – and instead... is blood all over the floors of this hospital. They say it’s as bad as a military warzone hospital."
He added: "Knives, knives, knives" – punctuating each word by miming a stabbing. "London hasn’t been used to that, they’re getting used to it. It’s pretty tough."
At least 36 people have been fatally stabbed in London since the beginning of the year and last month six were attacked with knives within 90 minutes.
But the figures pale in comparison to the 4 685 gun deaths and 8 301 gun injuries in the first four months of the year across the US.
Mr Trump also claimed that more guns could have prevented the Paris terrorist attacks.
Making a gun gesture with his fingers and shouting "boom", he told the audience that "if one employee or just one patron had a gun … or if one person in this room had been there with a gun the attackers would have been stopped". He added: "The terrorists would have fled or been shot and it would have been a whole different story."
More than 70 000 NRA members were expected to attend the conference. Mr Trump said in his speech that their Second Amendment rights were "under siege".
The President reiterated his call for teachers to be armed in schools. In his comments about London Mr Trump did not specify a particular hospital. But his claims are thought to relate to an interview in which Martin Griffiths, a surgeon at Barts Health NHS Trust, said children as young as 13 were being admitted for life-threatening wounds on a daily basis.
Mr Griffiths told Radio 4’s Today that colleagues who had served in the military likened their work at the London hospital to being at Camp Bastion, the British Forces base in wartorn Afghanistan.
Gun deaths in the US this year include the 17 people killed at Stoneman Douglas High School in Parkland, Florida – a massacre which has galvanised the anti-gun movement.