Sir Keir Starmer has condemned comments by Elon Musk suggesting that "civil war is inevitable" following violent unrest in the UK.
The owner of X, formerly Twitter, posted the remarks on the platform in response to a video showing people aiming fireworks at police.
The prime minister's spokesperson said there was "no justification" for Mr Musk's comments, adding there was more that social media companies "can and should be doing".