Donald Trump is facing criticism for retweeting the name of the alleged whistleblower whose complaint triggered the impeachment investigation into his dealings with Ukraine.
The US president, who has 68 million followers on Twitter, escalated his row with the Democrats by sharing a post from one of his supporters purporting to disclose the whistleblower's identity, including his son Donald.
Until now Mr Trump had refrained from tweeting information about the individual, whose name has been shared on social media by the president's conservative allies.
However, on Thursday he retweeted a post from his campaign "war room" which contained a link to an article in the conservative Washington Examiner with the alleged whistleblower's name in the headline.
The congressional impeachment investigation originated in the whistleblower's nine-page complaint alleging that Mr Trump put pressure on Ukrainian president Volodymyr Zelenskiy to announce he was investigating Hunter Biden, the son of former vice president Joe Biden and potential Democratic candidate in November's election.
While the original retweet has been deleted, the US president retweeted another posting naming the whistleblower and accusing him of committing perjury.
The whistleblower, who is understood to be a CIA analyst, enjoys legal protection under US law. The Telegraph has chosen not to disclose his identity.
His lawyers have sent a "cease and desist" letter to the White House warning that he and his family have been put in "physical danger" by the disclosures.
Mr Trump's offending tweet was part of a barrage which the US president has sent out in recent days as he intensified his attack on senior Democrats including Nancy Pelosi, the party's leader in the House of Representatives and Adam Schiff, chair of the House Intelligence Committee.
The US president's action was condemned by Stephen Kohn Chairman of the Board of Directors of the National Whistleblower Centre, who said naming the whistleblower would be committing a serious violation of the law.
"Whomever is responsible for retaliating against the whistleblower should be prosecuted to the fullest extent of the law," he added.
"Retaliation against the Ukraine whistleblower is unacceptable. There must be accountability, even if the person breaking the law is the President of the United States."
The Inspector General Act of 1978 bars a government watchdog who receives a complaint from disclosing the identity of that person without consent, unless it is deemed "unavoidable". The law appears not to bind others, such as the US president or his allies, from outing the whistleblower if the identity is discovered.