US President Donald Trump cannot block critics whose views he dislikes from following his Twitter account, a federal appeals court ruled on Tuesday.

In a 3-0 decision, the 2nd US Circuit Court of Appeals in Manhattan said the US Constitution's First Amendment forbids Trump from using Twitter's "blocking" function to limit access to his account, which is otherwise open to the public.

"The First Amendment does not permit a public official who utilizes a social media account for all manner of official purposes to exclude persons from an otherwise-open online dialogue because they expressed views with which the official disagrees," Circuit Judge Barrington Parker wrote.

The White House and the US Department of Justice did not immediately respond to requests for comment. Twitter had no immediate comment.

Trump has made his @RealDonaldTrump Twitter account a central, and controversial, part of his presidency, using it to promote his agenda, announce policies and attack critics. He has 61.8 million followers.

Tuesday's decision upheld a May 2018 ruling by US District Judge Naomi Reice Buchwald in Manhattan.

The Justice Department has called her ruling "fundamentally misconceived," saying Trump used Twitter in his personal capacity to disseminate his views, not to offer a platform for public discussion.

Trump's use of Twitter had been challenged by plaintiffs including the Knight First Amendment Institute at Columbia University. Its lawyers did not immediately respond to requests for comment.