US President Donald Trump has been accused of sinking to a new low after attacking a female news anchor with a series of highly personal and spiteful tweets.

President Trump took aim late Thursday night at Mika Brzezinski and Joe Scarborough, hosts of the MSNBC program Morning Joe, in a Twitter attack that has been condemned by fellow Republicans.

The President called Ms Brzezinski “low I.Q. Crazy Mika” and said she was “bleeding badly from a face-lift” when she visited his Mar-a-Lago property in Florida around New Year’s Eve.

He referred to Mr Scarborough, a former Republican congressman, as “Psycho Joe”.

I heard poorly rated @Morning_Joe speaks badly of me (don't watch anymore). Then how come low I.Q. Crazy Mika, along with Psycho Joe, came..

— Donald J. Trump (@realDonaldTrump) June 29, 2017

…to Mar-a-Lago 3 nights in a row around New Year's Eve, and insisted on joining me. She was bleeding badly from a face-lift. I said no!

— Donald J. Trump (@realDonaldTrump) June 29, 2017

The White House defended the attack in the face of an outpouring of criticism from both sides of US politics.

“The President has been attacked mercilessly on personal accounts by members on that program,” White House spokeswoman Sarah Huckabee Sanders told a news briefing Friday morning (AEST).

“And I think he’s been very clear that when he gets attacked he’s going to hit back.

“The American people elected someone who’s tough, who’s smart and who’s a fighter.

“And that’s Donald Trump. And I don’t think that’s a surprise to anybody that he fights fire with fire.”

Ms Brzezinksi, 50, hit back earlier by tweeting an advert for a breakfast cereal that bears the caption, “made for small hands” in an apparent reference to a taunt often directed at President Trump by his critics.

pic.twitter.com/8YhzcCUwM1

— Mika Brzezinski (@morningmika) June 29, 2017

President Trump is known for his prolific Twitter commentary, which has included mocking attacks on critics and rivals, but his latest tweets drew a particularly strong response.

Republican Senator Susan Collins, whose vote is considered critical to the success of the President’s health care plan, wrote on Twitter that Mr Trump’s Twitter tirades “has to stop”.

“We don’t have to get along, but we must show respect and civility,” she said.

This has to stop – we all have a job – 3 branches of gov’t and media. We don’t have to get along, but we must show respect and civility.

— Sen. Susan Collins (@SenatorCollins) June 29, 2017

Republican lawmakers and others sharply rebuked President Trump.

The tweets “represents what is wrong with American politics, not the greatness of America,” said Republican Senator Lindsey Graham, while another, Ben Sasse, called the remarks “beneath the dignity of your office.”

“I don’t see that as an appropriate comment,” Republican House of Representatives Speaker Paul Ryan said of the tweets.

Mr. President, your tweet was beneath the office and represents what is wrong with American politics, not the greatness of America.

— Lindsey Graham (@LindseyGrahamSC) June 29, 2017

MSNBC posted a tweet saying: “It’s a sad day for America when the president spends his time bullying, lying and spewing petty personal attacks instead of doing his job.”

On Thursday morning’s show (US time), Ms Brzezinski excoriated the Trump administration and said its officials should not act “lobotomised” because they are so scared of the President.

– With agencies