In a blistering statement, the union’s diplomatic mission in Washington also accused Mr Trump of dishonouring America by supposedly using foul language to describe Haiti, El Salvador and unspecified African nations during a discussion about immigration.
The Washington Mission of the African Union said the US President didn’t just need to apologise to Africans, he should be saying sorry to all people of African descent, all over the world.
It added to the pressure on Mr Trump by issuing a statement saying: “The African Union Mission wishes to express its infuriation, disappointment and outrage over the unfortunate comment made by Mr. Donald Trump, President of the United States of America, which remarks dishonour the celebrated American creed and respect for diversity and human dignity.
"The African Union Mission condemns the comments in the strongest terms and demands a retraction of the comment as well as an apology not only to Africans but to all people of African descent around the globe."
The Washington Mission’s demands follows earlier statements issued by the African Union from its headquarters in Addis Ababa, Ethiopia, in which the organisation reportedly made clear its “alarm” at Mr Trump’s “very racist” comments.
Spokeswoman Ebba Kalondo was quoted as saying: “Given the historical reality of how many Africans arrived in the United States as slaves, [Mr Trump’s] statement flies in the face of all accepted behaviour and practice.
“This is particularly surprising as the United States of America remains a global example of how migration gave birth to a nation built on strong values of diversity and opportunity.
“We believe that a statement like this hurts our shared global values on diversity, human rights and reciprocal understanding."
The African Union demand for an apology is likely to add to the intense pressure on Mr Trump following reports of what he said in the White House on Thursday during a discussion about immigration.
After being presented with a proposal to restore protections for immigrants from Haiti, El Salvador and African countries, Mr Trump reportedly demanded: “Why are we having all these people from sh**hole countries come here?”
He was also said to have added the suggestion that the US should admit people from Norway instead.
Mr Trump did not initially challenge the comments, but after they were heavily criticised by diplomats, rival politicians and members of his own party, he took to Twitter to deny he had ever used the phrase “sh**hole countries”.
This, however, provoked a stinging rebuke from Democratic Senator Dick Durbin, who insisted he had been present at the meeting and heard the president using such foul language.
Mr Durbin said: “The President started tweeting this morning, denying that he used those words. It is not true. He said these hate-filled things, and he said them repeatedly.
“In the course of his comments he said things that were hate-filled, vile and racist ... I cannot believe that in the history of the White House, in that Oval Office, any president has ever spoken the words that I personally heard our president speak.”
Mr Durbin added: “When the question was raised about Haitians for example… he said ‘Haitians, do we need more Haitians?’
“And then he went on to describe the immigration from Africa that was being protected in this bipartisan measure. That’s when he used these vile and vulgar comments, calling the nations they come from ‘sh**holes’ - the exact word used by the President not just once, but repeatedly.”
Mr Durbin said he told Mr Trump the word “chain migration” – used by opponents of immigration to describe people sponsoring family members to join them in the US - was “painful” for many African-Americans whose ancestors had arrived in the US as slaves.
According to the senator, the president’s response was simply to respond: “That’s a good line”.
In his tweeted denial, Mr Trump said: “The language used by me at the meeting was tough, but this [sh**hole] was not the language used.”
He insisted he had “never said anything derogatory about Haitians other than Haiti is, obviously, a very poor and troubled country”, and added: “Made up by Dems. I have a wonderful relationship with Haitians. Probably should record future meetings - unfortunately, no trust!”
The language used by me at the DACA meeting was tough, but this was not the language used. What was really tough was the outlandish proposal made - a big setback for DACA!— Donald J. Trump (@realDonaldTrump) January 12, 2018
On Friday, however, at the end of a ceremony in which he signed a proclamation in honour of the civil rights leader Martin Luther King Jr, reporters asked Mr Trump if he was going to apologise, with veteran black journalist April Ryan enquiring: “Mr. President, are you a racist?"
Mr Trump ignored the questions and Ms Ryan, with whom he has previously had some notable interactions.
During a press conference last February, Mr Trump asked her if she would set up a meeting for him with members of the Congressional Black Caucus.