President Donald Trump was accused of using "hate-filled, vile and racist" language in the Oval Office after he reportedly attacked immigrants coming to the United States from "s---hole countries".
Mr Trump denied making the comments about immigrants from Africa, Haiti and El Salvador, saying he had been "tough, but this was not the language used".
A group of 54 "extremely appalled" African countries demanded he retract and apologise for his reported comments.
After an emergency session to weigh Mr Trump's remarks, the group of African ambassadors to the United Nations said it was "concerned at the continuing and growing trend from the US administration toward Africa and people of African descent to denigrate the continent and people of colour."
The group is "extremely appalled at, and strongly condemns the outrageous, racist and xenophobic remarks by the president of the United States of America as widely reported by the media," a statement added, demanding a "retraction and an apology."
It came after the United Nations human rights office decried the remarks - which were reported by the Washington Post - as "racist".
In an extraordinary rebuke, UN human rights spokesman Rupert Colville told a Geneva news briefing on Friday morning that the US president's alleged comments "encouraged racism and xenophobia".
"These are shocking and shameful comments from the President of the United States. There is no other word one can use but 'racist'," Mr Colville said.
"You cannot dismiss entire countries and continents as 's---holes', whose entire populations, who are not white, are therefore not welcome," he added.
The issue was more than "vulgar language", Mr Colville said.
"It's about opening the door to humanity's worst side, about validating and encouraging racism and xenophobia that will potentially disrupt and destroy lives of many people."
Mr Trump had also failed to clearly condemn the "anti-Semitic and racist actions of white supremacists in Charlottesville" at a rally in Virginia last August, Mr Colville said
Mr Trump had convened a meeting at the White House on Thursday to discuss reforming immigration policy, and one of the politicians inside the Oval Office suggested that a deal could be reached if Mr Trump agreed to restore protection for immigrants from Haiti, El Salvador and African countries.
“Why are we having all these people from s---hole countries come here?” the president responded, according to two people who spoke to The Washington Post. The paper said he was referring to African countries, Haiti and El Salvador.
"This is ignorance ... to speak in such vile racist terms."— MSNBC (@MSNBC) January 12, 2018
Rep. @LuisGutierrez reacts to Trump's 'sh**hole countries' remark, says "the paint has been stripped away from Donald Trump." pic.twitter.com/US4Amyx4U5
He then reportedly suggested that the United States should instead bring more people from countries like Norway, whose prime minister he met on Wednesday.
His remarks reportedly left the assembled politicians “taken aback”, the paper said, with Lindsey Graham, the Republican senator for South Carolina, and Dick Durbin, Democratic senator for Illinois, among those in the room.
Here is my statement on the President’s comments today: pic.twitter.com/EdtsFjc2zL— Rep. Mia Love (@RepMiaLove) January 11, 2018
Mr Durbin said Mr Trump had used the reported words.
The senator said: "In the course of his comments he said things that were hate-filled, vile and racist. I use those words advisedly, I understand how powerful they are.
"I cannot believe that, in the history of the White House and that Oval Office, any president has ever spoken the words that I personally heard our president speak yesterday."
Mr Graham said: "Following comments by the president I said my piece directly to him yesterday. The president and all those attending the meeting know what I said and how I feel."
Hillary Clinton, on Twitter, accused Mr Trump of having "ignorant, racist views of anyone who doesn’t look like him".
Congressman Luis Gutierrez said: "We always knew that President Trump doesn't like people from certain countries or people or certain colours.
"We can now we say with 100 per cent confidence that the president is a racist who does not share the values enshrined in our Constitution."
Asked about the remarks, White House spokesman Raj Shah said:
"Certain Washington politicians choose to fight for foreign countries, but President Trump will always fight for the American people," he said.
Republican Rep. Mia Love of Utah, the daughter of Haitian immigrants, said Mr Trump's comments were "unkind, divisive, elitist and fly in the face of our nation's values."
Haiti’s ambassador to the United States, Paul G. Altidor, said that “the president was either misinformed or miseducated about Haiti and its people.”
Leading academics also condemned Mr Trump. “The notion that all immigrants from certain nations are a drag on the US economy is unsupported. The notion that all students from a certain nation think and behave in the same way is equally unacceptable,” said British born John Quelch, the dean of Miami Business school.
Mr Trump has called himself the "least racist person that you've ever met."
On Friday he signed a proclamation honouring Martin Luther King Day.
In a speech at the event Mr Trump said: "No matter what the colour of our skin, or the place of our birth, we are all created equal."
As he left the room the president was asked several times by journalists "Are you a racist?" but refused to answer.
Earlier, Mr Trump spoke to The Wall Street Journal, and claimed that he has developed a positive relationship with North Korea’s leader.
“I probably have a very good relationship with Kim Jong-un, ”said Mr Trump, despite there being no formal contact between US and North Korean officials in decades.
Asked if he has spoken with Mr Kim, Mr Trump replied: “I don’t want to comment on it. I’m not saying I have or haven’t. I just don’t want to comment.”
The president has called the nation’s leader a “maniac,” a “bad dude,” mocked him as “short and fat,” and referred to him repeatedly as “rocket man.” Mr Kim in response has warned he would “tame the mentally deranged US dotard with fire”.
Mr Trump told the paper, however, that his Twitter insults were simply part of his game plan.
“You’ll see that a lot with me,” he said about combative tweets. “And then all of the sudden somebody’s my best friend. I could give you 20 examples. You could give me 30. I’m a very flexible person.”
The president said he approved of North Korea’s participation in next month’s Olympic Games, and acknowledged that Pyongyang may be trying to separate Washington and Seoul.
“If I were them, I would try,” he said. “The difference is I’m president, other people aren’t. And I know more about wedges than any human being that’s lived.”
Mr Trump also announced for the first time that Mexico could pay for the border wall through negotiations to revise the North American Free Trade Agreement.
“They can pay for it indirectly through Nafta,” he said. “We make a good deal on Nafta, and, say, I’m going to take a small percentage of that money and it’s going toward the wall. Guess what? Mexico’s paying.”