LONDON — If anyone had any hope that President Trump would adopt a more conciliatory tone toward Britain before his visit in July, it was dashed on Friday, when he appeared before a National Rifle Association conference in Dallas and took a jab at London’s crime rate.

“Knives, knives, knives, knives,” he said, mimicking a stabbing motion as he defended gun ownership in the United States.

Saying that Americans’ rights to carry guns were “under siege,” he said: “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 horrible stabbing wounds.”

Appearing to link the wave of knife crimes in London to a ban on guns, he added: “They don’t have guns. They have knives, and instead there’s blood all over the floors of this hospital.”