Comparing the USA to the United Kingdom, he said a top hospital in the capital was like a "military warzone hospital" despite "unbelievable tough gun laws".
In a speech at the NRA convention in Dallas on Friday, Trump said he 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 disgusting stabbing wounds".
Trump, who is due to visit Britain on July 13, told NRA members that a "once very prestigious" London hospital, which he did not name, had become overwhelmed with victims of knife attacks. "Gunshot wounds are at least twice as lethal as knife injuries and more hard to fix", Brohi said in the statement on Saturday.
"They say it's as bad as a military war zone hospital", Trump said.
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.
Dr. Karim Brohi, another Royal London surgeon, said that while it is true that there is knife violence in London which must be addressed "urgently and at all levels", no potential solution involves the use of guns.
'And instead there's blood all over the floors of this hospital.
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London has seen 12,980 knife crimes committed in the capital during 2017 which is up 2,452 on the year before.
London's Metropolitan Police said last month that it's investigating the cause of the increase in murders, but said the city remains among the safest in the world.
There have been growing concerns over knife crime after figures a year ago showed such attacks had reached the highest point in England and Wales since 2011, the earliest date for which comparable data are available.
London Mayor Sadiq Khan, who has previously clashed with the U.S. president over Mr Khan's response to terrorism, declined to comment on Mr Trump's latest comments.
The US ambassador to Britain, Woody Johnson, said Mr Trump would "definitely" be coming to London, despite the warnings of likely demonstrations.
Mr Trump linked a rise in recorded crime in England and Wales last October with the "spread of radical Islamic terror".
After a high school shooting in Parkland, Florida, left 17 dead in February, Mr Trump said he would "fight" the NRA on gun control.
Mr Trump also thanked Kanye West, the rapper, for his public support.