He told the National Rifle Convention (NRA) in Dallas: "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 frightful stabbing wounds".
"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 frightful stabbing wounds".
"That just, it's just obvious".
Karim Brohi, a trauma surgeon at the Royal London Hospital, said in a statement on Saturday that while knife violence was "a serious issue" in London, "to suggest guns are part of the solution is ridiculous".
Speaking at a pro-gun rally, the USA president claimed that knife crime in London is so bad that one unnamed hospital in the capital is "like a war zone for terrible stabbing wounds" with "blood all over the floors".
He added: "Knives, knives, knives" - punctuating each word by miming a stabbing.
Donald Trump attacked London over knife crime on Friday.
Ex-lord chancellor and justice secretary Charlie Falconer also dismissed President Trump's claims that London was a hotbed of crime and a war zone, explaining succinctly that Trump's barrage of comments about the affairs of London would hardly help relations between the United States and the city. "London hasn't been used to that, they're getting used to it".
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In February, London's monthly murder rate overtook New York's for the first time (15 to 14) - though NY had seen more murders in 2018 overall if January's figures are included.
The US President did not clarify which story he was talking about, and which hospital he was referring to.
And several current and former British politicians noted the difference in murder rates - 4.88 per 100,000 in the U.S. each year, as opposed to 0.92 per 100,000 in the UK. Another surgeon at the hospital noted in a tweet that "gunshot wounds are at least twice as lethal as knife injuries and more hard to fix".
Trump is slated to visit the United Kingdom in July for a working visit with Prime Minister Theresa May.
It is unclear whether Trump was refering to the interview with Griffiths in his speech.
At the NRA convention, Trump also suggested that a coordinated extremist attack on Paris in 2015 that claimed 130 lives would have been far less deadly if Parisians had been carrying guns to protect themselves.
Referring to London in his NRA speech, Mr Trump, had said they don't have guns.
Trump has criticized London's Metropolitan Police and Mayor Sadiq Khan, a Muslim, on several occasions.