'Child should be kept out of politics': Melania rebukes scholar who named her son during impeachment hearing

US First Lady Melania Trump on Wednesday (local time) lashed out at a Democrat impeachment witness Professor Pamela Karlan who made a reference to Melania and Donald Trump's son Barron in a joke she made while answering questions.

"A minor child deserves privacy and should be kept out of politics. Pamela Karlan, you should be ashamed of your very angry and obviously biased public pandering, and using a child to do it," the First Lady said in a rare political tweet aimed directly at Stanford Law professor Pamela Karlan, an impeachment witness for House Democrats.

The First Lady was addressing Karlan's mention of Barron Trump in her testimony, wherein she used the 13-year-old's first name in an analogy to make an argument about the differences between kings and presidents.

"The Constitution says there can be no titles of nobility, so while the President can name his son Barron, he can't make him a baron," said Karlan, who is in favour of the President being impeached.

The pun led to chuckles in the congressional hearing room, but Melania Trump made clear it was no laughing matter.

Karlan, however later apologised for her remark, saying, "I want to apologise for what I said earlier about the President's son, it was wrong of me to do that. I wish the President would apologise, obviously, for the things he's done that's wrong, but I do regret having said that."

It was the first time when the First Lady has weighed in publicly on the ongoing impeachment inquiry and investigation into her husband.

Asked about Trump's tweet, White House press secretary Stephanie Grisham told CNN, "I think Mrs. Trump's tweet speaks very clearly for itself."

Trump also retweeted his wife's message to his 67 million followers.