Donald Trump has tweeted a response to this morning's incident in Westminster, in which a car drove into barriers outside the House of Lords.
His tweet, in which he said "these animals are crazy", immediately sparked criticism.
"Another terrorist attack in London...These animals are crazy and must be dealt with through toughness and strength!" he wrote.
The Metropolitan Police have announced that counter-terror forces are investigating the incident, but have not confirmed that it was terror-related or released the identity or motive of the suspect.
A man in his 20s, the driver of the vehicle, was detained at the scene and is in custody.
Motorsport reporter Simon Patterson replied to Trump's tweet: writing: "Nothing like calling people ‘animals’ to keep them feeling like it’s us and them. F*** off and deal with your own issues, you tangerine facist."
There was speculation among the replies that the crash was the work of a Jihadi - but the police have not released any information about the incident beyond the fact that they've detained the suspect and are investigating it.
There is no suggestion at present that the driver was a Jihadi.
Another Twitter user ran a poll asking people to decide whether they thought Donald Trump or terrorists were a bigger threat to democracy.