U.S. President Donald Trump on Sunday assailed a group of Democratic congresswomen of colour as foreign-born troublemakers who should go back to the "broken and crime-infested places from which they came," ignoring the fact that the women are American citizens and all but one were born in the U.S.

Trump's tweets drew sharp rebukes from Democrats, who derided his remarks as racist. House Speaker Nancy Pelosi said the president wants to "make America white again."

Meantime Republican Rep. Justin Amash of Michigan, a Trump critic who recently took steps to leave his party, called the remarks "racist and disgusting."

Trump was almost certainly referring to Rep. Alexandria Ocasio-Cortez of New York and her allies in what's become known as "the squad." The others are Reps. Ilhan Omar of Minnesota, Ayanna Pressley of Massachusetts and Rashida Tlaib of Michigan. Only Omar was born outside the U.S., in Somalia.

Ocasio-Cortez swiftly denounced his remarks. "Mr. President, the country I 'come from' & the country we all swear to, is the United States," she tweeted.

With his remarks, Trump again inserted himself into a rift between Pelosi and the liberal congresswomen, after offering an unsolicited defence of the Democratic speaker days earlier. Pelosi has been seeking to minimize Ocasio-Cortez's influence in recent days, prompting Ocasio-Cortez to accuse Pelosi of trying to marginalize women of colour. "She is not a racist," Trump said Friday.

Mr. President,<br><br>As Members of Congress, the only country we swear an oath to is the United States. <br><br>Which is why we are fighting to protect it from the worst, most corrupt and inept president we have ever seen. <a href="https://t.co/FBygHa2QTt">https://t.co/FBygHa2QTt</a> —@IlhanMN

On Sunday, Trump's tone changed.

"So interesting to see 'Progressive' Democrat Congresswomen, who originally came from countries whose governments are a complete and total catastrophe, the worst, most corrupt and inept anywhere in the world (if they even have a functioning government at all), now loudly and viciously telling the people of the United States, the greatest and most powerful nation on earth, how our government is to be run," he said in tweets. "Why don't they go back and help fix the totally broken and crime-infested places from which they came."

He added: "These places need your help badly, you can't leave fast enough. I'm sure that Nancy Pelosi would be very happy to quickly work out free travel arrangements!"

Democratic Rep. Rashida Tlaib of Michigan, centre, gestures while testifying before the House oversight committee hearing on family separation on Friday as Democratic Rep. Ayanna Pressley of Massachusetts, right, and Ocasio-Cortez look on. (Pablo Martinez Monsivais/Associated Press)

Trump's tweets came just days after three members of the group of four progressive Democrats gave emotional testimony about the conditions they witnessed when they visited border facilities earlier this month.

Tlaib called the government's family separation policy an intentional and cruel strategy "created by the Trump administration dead set on sending a hate-filled message that those seeking refuge are not welcome in our America."

"We do have a crisis at our border; it is one of morality," she said.

The attacks may also 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 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.

"Unfortunately there is an American tradition of telling people to go back where they came from," New York City Mayor Bill de Blasio, a Democratic presidential contender, said on CNN's State of the Union. "It's a very bad tradition that we need to weed out of our nation because we are a nation of immigrants, that is who we are by our nature for hundreds of years. But you don't expect to hear it from the president."

Accused of racism

It was far from the first time that 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 United States. In his campaign kickoff in June 2015, he deemed many Mexican immigrants "rapists." And last year, during a White House meeting on immigration, he wondered why the United States was admitting so many immigrants from "shithole countries" like Haiti, El Salvador and several African nations.

Ocasio-Cortez, who is of Puerto Rican descent, was born in the Bronx, New York, and raised in suburban Westchester County.

Pressley, the first black woman elected to the House from Massachusetts, was born in Cincinnati.

Omar, the first Somali native elected to Congress and one of its first Muslim women, was born in Somalia but spent much of her childhood in a Kenyan refugee camp as civil war tore apart her home country. She immigrated to the United States at age 12, teaching herself English by watching American TV and eventually settling with her family in Minneapolis.

Tlaib was born in Detroit.