US president Donald Trump is being sued by people he blocked on Twitter who claim that was a violation of their right to free speech under the US Constitution.

The unprecedented case has been brought by the Knight First Amendment Institute at Columbia University, and named seven individuals rejected from Mr Trump's account after criticising him.

Also being sued are the White House Press Secretary Sean Spicer and Dan Scavino, the White House director of social media.

Lawyers for the plaintiffs contend that Mr Trump's tweets amount to official statements by the President of the United States. Mr Spicer has previously said they should be treated as such.