President Donald Trump has sparked outrage on both sides of politics after posting a series of “incredibly racist” tweets telling congresswomen of ethnic backgrounds to “go back” to their home countries.

On Sunday, Mr Trump took aim at a group of unnamed Democrats, “who originally came from countries whose governments are a complete and total catastrophe”.

His scathing attack is believed to have been targeting a group of newly elected members who call themselves “The Squad”.

The so-called Squad include Alexandria Ocasio-Cortez of New York; Ayanna Pressley of Massachusetts; Rashida Tlaib of Michigan; and Ilhan Omar of Minnesota.

He called on the women of colour, who are American citizens and all but one was born in the US, to “go back and help fix the totally broken and crime infested places from which they came”.

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……

— Donald J. Trump (@realDonaldTrump) July 14, 2019

It came amid a week of escalating tensions between the four and House Speaker Nancy Pelosi. 

Ms Pelosi 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 strongly rebuked Mr Trump’s tweets, accusing the president of wanting to “make America white again” and calling 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.

Our diversity is our strength and our unity is our power. https://t.co/ODqqHneyES

— Nancy Pelosi (@SpeakerPelosi) July 14, 2019

Senator Bernie Sanders, a key ally of the Squad, tweeted: “When I call the president a racist, this is what I’m talking about.”

When I call the president a racist, this is what I'm talking about

We must stand together for justice and dignity towards all. https://t.co/lweeJk7NoF

— Bernie Sanders (@BernieSanders) July 14, 2019

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

US representative Nanette Barraga also condemned Mr Trump, calling his words “incredibly racist”.

With his remarks, Mr Trump again inserted himself into a rift between Ms Pelosi and the liberal congresswomen, after offering an unsolicited defence of the Democratic Speaker days earlier.

Ms Pelosi has been seeking to minimise Ms Ocasio-Cortez’s influence in recent days, prompting Ms Ocasio-Cortez to accuse Ms Pelosi of trying to marginalise women of colour. “She is not a racist,” Mr Trump said on Friday.

“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!”

-with AAP