US President Donald Trump has claimed an unnamed hospital in London is "like a war zone for horrible stabbing wounds".
He made the comment before miming a stabbing motion during an address at the National Rifle Association convention in Dallas.
Mr Trump told the NRA: "Yes that's right, they don't have guns, they have knives and instead there's blood all over the floors of this hospital."
In an extraordinary address, Mr Trump also claimed that the 2015 Paris terror attack, in which 130 were killed, could have been stopped had the victims been armed with guns.
He said: "If one employee or just one patron had a gun… or if one person in this room had been there with a gun... the terrorists would have fled or been shot and it would have been a whole different story."
He earlier gained cheers for telling the NRA his administration was "fighting to protect your Second Amendment, and we will protect your Second Amendment" right to bear arms.
The president told tens of thousands of attendees that their right to bear arms was “under siege”.
But he pledged that those rights “will never, ever be under siege as long as I’m your president”.
Trump did not elaborate on how the Second Amendment was under siege.
The president's comment that a London hospital is "like a war zone" is likely to cause anger in Britain, with many planning demonstrations when he visits in July.
The US president has been warned to expect protests during the controversial trip, which will be a “working visit” rather than a full-blown state occasion.
The president was addressing the NRA gathering nearly three months after a deadly shooting at a high school in Parkland, Florida.
The president temporarily strayed from the group’s strong opposition to tougher gun controls after the school shooting – only to rapidly return to the fold.
He was speaking at the event for the fourth year in a row. Last year, he became the first sitting president to appear in more than 30 years, declaring that the “assault” on the Second Amendment had ended.
But this year’s speech in Dallas came as the issue of gun violence takes on new urgency after one of the deadliest school shootings in US history.
Survivors of the February 14 shooting at Marjory Stoneman Douglas High School that left 17 people dead are leading a massive national gun control movement.
Several groups have announced plans to protest over the weekend during the NRA event. The protesters will include parents of those killed in Parkland and other shootings.
The survivors’ campaign has not led to major changes from the White House or the Republican-led Congress but Mr Trump did briefly declare he would stand up to the powerful gun lobby.
He later backpedalled, expressing support for modest changes to the background check system, as well as arming teachers.
His attendance at this year’s NRA convention was announced just days ago and came after Vice President Mike Pence was already scheduled to appear.
Asked why Mr Trump was attending, given political tensions around gun violence, White House press secretary Sarah Huckabee Sanders said this week that safety was a “big priority”.