US President Donald Trump has claimed an unnamed hospital in London is "like a war zone for horrible stabbing wounds".

He made the extraordinary 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."

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 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".

"We also support the Second Amendment, and strongly support it, and don't see there to be a problem with speaking at the National Rifle Association's meeting," she said.

Mr Trump has long enjoyed strong backing from the NRA, which spent about 30 million US dollars (£22 million) supporting his presidential campaign.

One of the Parkland survivors, David Hogg, was critical of the president's planned attendance.

"It's kind of hypocritical of him to go there after saying so many politicians bow to the NRA and are owned by them," he said. "It proves that his heart and his wallet are in the same place."

Trump's moves have drawn concerns from both sides of the gun debate.

"He ran as supposedly the best friend of the Second Amendment and has become gun grabber in chief," said Michael Hammond, legislative counsel to the Gun Owners of America.

He said his members were upset Mr Trump had approved a spending bill that included background check updates. "We're not confident at all. We are very disappointed," he said.