'The squad' are 'very racist, not very smart', tweets Donald Trump

President Donald Trump has lashed out again at four Democratic congresswomen at the centre of the race row gripping US politics, labelling them "very racist" and "not very smart".

In a tweet posted overnight, Mr Trump took aim at "the squad", a quartet of congresswomen who represent the left of the Democratic caucus.

"The 'Squad' is a very Racist group of troublemakers who are young, inexperienced, and not very smart. They are pulling the once great Democrat Party far left, and were against humanitarian aid at the Border...And are now against ICE and Homeland Security. So bad for our Country!” Mr Trump wrote.

The tweet was posted while the president was in a motorcade on his way to pay his respects to Supreme Court Justice John Paul Stevens, who died last week.

It was Mr Trump’s latest salvo in the racism row triggered by the president’s tweets earlier this month telling non-white congresswomen Alexandria Ocasio-Cortez, Ayanna Pressley, Ilhan Omar and Rashida Tlaib to “go back to where you came from”.

Ms Omar was born in Somalia and became a US citizen as a teenager. All the other members of "the squad" were born in the United States.

Mr Trump’s original comment generated widespread condemnation and censure by the Democrat-controlled House of Representatives. He denies being racist.

In his latest tweet, Mr Trump did not elaborate on why he feels the four congresswomen were "very racist" and "not very smart".

Mr Trump stood silently during a rally last week as a crowd repeatedly chanted "send her back" about Ms Omar.

He later described the crowd as "incredible patriots".

The congresswomen in recent days have stepped up their attack on Mr Trump over the comments.

"You all should end this charade and accept that this racist president wants every black/brown person deported and Muslims banned," Ms Omar tweeted at the weekend.

Ms Ocasio-Cortez has Puerto Rican ancestry, Ms Pressley is African-American and Ms Tlaib's parents were born in Palestine.

"I'm not going nowhere, not until I impeach this president," Ms Tlaib said in a speech yesterday.

Ms Ocasio-Cortez was greeted with shouts of "Welcome home" at an event overnight in Queens, the New York borough she represents and where Mr Trump grew up.

"Once you start telling American citizens to quote ‘go back to their countries,’ this tells you that this president’s policies are not about immigration, it’s about ethnicity and race,” she said.

"His biggest mistake was that he said the quiet part loud."

Workplace harassment guidelines written by the US government specifically include the phrase "go back to where you came from" as an example of racism.

Who are the squad?

Alexandria Ocasio-Cortez, Rashida Tlaib, Ilhan Omar and Ayanna Pressley are among the most junior members of Congress.

Elected in November last year, the four are new to Washington politics.

But thanks to substantial social media followings and an inclination to be brash and outspoken, they wield significant influence within the Democratic Party.

The four are informally referred to as "the squad".

They also represent the far-left of the caucus, with Ms Ocasio-Cortez and Ms Tlaib identifying as "Democratic socialists".

The four draw a sharp contrast to the Republican caucus of the House of Representatives, who have just 13 women and a mere handful of non-white members.

The squad had been quibbling with Democratic Speaker Nancy Pelosi over the weekend over social media, but the animus was redirected after Mr Trump's tweets.

"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," Ms Pelosi said.

"Our diversity is our strength and our unity is our power."

Who is Alexandria Ocasio-Cortez?

The best known of the four, Alexandria Ocasio-Cortez stunned Washington DC last year when she ousted Democratic heavyweight Joe Crowley in a primary election.

Mr Crowley was feted as the next Speaker of the House, but was caught unaware by Ms Ocasio-Cortez, who was working as a bartender before her election to Congress.

The youngest-ever congresswoman, 29-year-old Ms Ocasio-Cortez represents parts of The Bronx and Queens in New York.

But in a few short months she has become a household name in America, one of the best-known and most divisive politicians in the country.

She has long been a proponent of major government action to take on climate change and health care, branded as the "Green New Deal and "Medicare-for-All".

Who is Rashida Tlaib?

Rashida Tlaib was one of the two first Muslim women to serve in Congress when she was sworn in in January. The other is Ilhan Omar.

Ms Tlaib represents one of the poorest districts in America, a part of Detroit so strongly Democratic that she was elected unopposed in November.

On her first day in Congress she drew controversy for a fiery speech she gave about Mr Trump.

"We gonna go in there and impeach the motherf---er," she said.

Who is Ilhan Omar?

Along with Ms Tlaib, Ilhan Omar was the first Muslim woman to be elected to Congress.

Ms Omar was born in Somalia but fled during the civil war, arriving in the USA in 1992.

She now represents a district in Minneapolis, Minnesota, after being voted in last year.

As a hijab-wearing black woman, Ms Omar has been subject to particularly nasty internet rumours, including that she married her own brother.

She has spoken sharply in criticism of Israel, with several comments of hers labelled as anti-Semitic.

Who is Ayanna Pressley?

Ayanna Pressley was elected to a seat in Boston, Massachusetts after ousting long-time incumbent Michael Capuano in the primary.

A heavily Democratic district that was previously represented by John F. Kennedy, Ms Pressley ran unopposed in the general election.

The win made her the first African-American woman elected to Congress from Massachusetts.

In her primary victory speech, she declared Mr Trump a "racist, misogynistic, truly empathy-bankrupt man".

Read more: Theresa May condemns Trump's racist tweets

Read more: Trump wants to 'make America white again': Pelosi