Twitter is citing “newsworthiness” and the public interest as reasons why it didn't remove United States (US) President Donald Trump's declaration in a tweet that North Korean leaders may not “be around much longer.”

On Saturday, after North Korea's foreign minister called Trump a “mentally deranged man” at the United Nations General Assembly in response to the latter's threatening speech, the US president responded on Twitter.

Twitter's rules state users “may not make threats of violence or promote violence, including threatening or promoting terrorism".

Twitter responded to questions about the policy on Monday, saying in a series of messages on its public policy account that “newsworthiness” is one of the factors it considers in determining if a tweet breaks the platform's rules.

It says the policy has been internal, but its public-facing rules will be updated to reflect it.