Outgoing British Prime Minister Theresa May on Tuesday called US President Donald Trump’s tweets telling progressive Democrat congresswomen to “go back” where they came from “completely unacceptable”.

“Her view is that the language which was used to refer to the women was completely unacceptable,” Ms May’s spokesman told reporters.

Mr Trump told a group of mostly American-born Democratic congresswomen to “go back and help fix the totally broken and crime infested places from which they came” – a comment that was condemned by Democrats as racist.

“So interesting to see ‘Progressive’ Democrat Congresswomen, who originally came from countries whose governments are a complete and total catastrophe… viciously telling the people of the United States… how our government is to be run,” Mr Trump said in a series of three comments on Twitter.

While he did not mention names, Mr Trump appeared to be referring to first-year Representatives Alexandria Ocasio-Cortez of New York, Ilhan Omar of Minnesota, Ayanna Pressley of Massachusetts, and Rashida Tlaib of Michigan – a group known as “the squad” that has been openly critical of both Mr Trump and the current Democratic leadership of the House.

Only Ms Omar, whose family left Somalia as refugees and arrived in Minneapolis in 1997, was born outside the US.

“Mr President, the country I ‘come from,’ and the country we all swear to is the United States,” Ms Ocasio-Cortez, like Mr Trump a native of New York City, responded on Twitter.

“You are angry because you can’t conceive of an America that includes us. You rely on a frightened America for your plunder.”

House Speaker Nancy Pelosi, a California Democrat, has feuded with the group in an increasingly bitter intra-party fight but came to their defence on Sunday along with other Democratic colleagues.

She called Mr Trump’s comments “xenophobic”.

“When @realDonaldTrump tells four American Congresswomen to go back to their countries, he reaffirms his plan to ‘Make America Great Again’ has always been about making America white again,” she said on Twitter.

“Do I fit into the President’s category?” US Senator Dick Durbin on Illinois, said on CBS’s “Face the Nation”, citing his family’s Lithuanian heritage.

“Thank goodness,” he said of Ms Omar’s journey from refugee to one of only two Muslim women elected to Congress, along with Ms Tlaib, a native of Detroit. 

“That is what America holds as a dream. The president should not diminish it.”

The attacks may have been meant to further the divides within the Democrat caucus, strained over internal debates on liberal policies and on whether to proceed with impeachment proceedings against Mr Trump.

Instead, Democrats as one voice denounced the comments, which evoked the old racist trope of telling a black person to go back to Africa.

“Let’s be clear about what this vile comment is: A racist and xenophobic attack on Democratic congresswomen,” tweeted Senator Elizabeth Warren, a Democratic presidential candidate.

Another 2020 contender, Beto O’Rourke, tweeted at the president: “This is racist. These congresswomen are every bit as American as you – and represent our values better than you ever will.”

Few Republicans immediately weighed in on the president’s comments. Shortly after the tweets, and a later post defending the harsh scenes at a border detention facility where hundreds of migrant men are being held in sweltering, foul-smelling conditions, Mr Trump left the White House to go golfing at his Virginia club.

It was far from the first time that Mr Trump has been accused of holding racist views.

His political career was launched on the backs of falsely claiming that President Barack Obama was not born in the US. In his campaign kick-off in June 2015, he deemed many Mexican immigrants “rapists”. And last year, during a White House meeting on immigration, he wondered why the US was admitting so many immigrants from “s***hole countries” like Haiti, El Salvador and several African nations.

With additional reporting from AAP and Reuters