More than 150 years after the abolition of slavery and more than 50 years after the passage of the Civil Rights Act, President Donald Trump's incendiary comments about immigrants have ripped open a jarring debate in the United States and around the world: Is the American president racist?

To Democrats and some historians, there is little dispute given the president's own words and actions. His political rise was powered first by his promotion of lies about Barack Obama's citizenship, then by his allegations that Mexican immigrants to the United States were rapists and murderers.

During a private meeting with lawmakers Thursday, he stunningly questioned why the US would admit Haitians or people from "s...hole" countries in Africa, expressing a preference instead for immigrants from Norway, a majority white nation.

AP US President Donald Trump says he's the "least racist person there is", but a presidential historian says the US hasn't had such a racist leader since Woodrow Wilson 97 years ago.

"President Trump said things that were hate-filled, vile and racist," said Senator Dick Durbin, Democrat-Illinois, who attended the meeting and confirmed the president's comments.

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On Friday, few Republicans defended the president's remarks, and party leaders were silent most of the day. Those who did speak out argued the comments were merely unvarnished statements on the economic blight in some regions of the world, not an expression of racial preference. Others said Trump, a 71-year-old who relishes rejecting political correctness, was voicing views held quietly by many.

A group of African ambassadors to the UN condemn US President Donald Trump's "xenophobic" comments and call for a retraction.

"I've said all along the president many times says what people are thinking," Republican Representative Jim Renacci, a candidate for Senate in Ohio, told Fox News.

"Let's judge the president after what we've done. Let's not judge the president on what he says."

Trump has repeatedly denied he is a racist, declaring during the 2016 campaign that he was the "least racist person there is".

AP Historian Douglas Brinkley said Trump's recent comments stand out from those other presidents. "No president has been so racially insensitive and shown outright disdain for people who aren't white."

On Friday (Saturday, NZ time), he offered a vague denial of his comments to lawmakers, tweeting that he said nothing "derogatory" about Haitians. He did not address the reports that he disparaged African nations and ignored questions about the comments from reporters.

Yet there's no doubt that the episode has added new fuel to the charges of racism that have dogged Trump for years, since long before he assumed the presidency.

In the 1970s, the federal government twice sued Trump's real estate company for favouring white tenants over blacks. He aggressively pushed for the death penalty for a group of black and Latino teenagers who were accused of raping a white woman in Central Park but later exonerated.

Now, as president, Trump's words carry the weight of an office that has long helped guide the nation's moral compass and defined the American ideal for millions around the world.

Although the United States has a complicated racial history, including slavery, segregation and persistent economic disparities between whites and minorities, Trump's most recent predecessors from both parties have used their position to promote equality and have endorsed immigration policies that brought millions of people from Africa and Latin America to the US.

"What Trump is doing has popped up periodically, but in modern times, no president has been so racially insensitive and shown outright disdain for people who aren't white," said Douglas Brinkley, a presidential historian.

AP Timothy Naftali, a presidential historian and former director of Richard Nixon's presidential library, says Trump's recent comments "shows the president is using language that implies he's thinking like a racist while making immigration policy".

Brinkley said Trump was the most racist president since Woodrow Wilson, who served from 1913 until 1921.

Wilson supported segregation, including in the federal government, and his policies are blamed for rolling back progress for the emerging black middle class in the nation's capital at the turn of the 20th century.

Decades after Wilson left office, President Richard Nixon made inflammatory comments about blacks, Jews and others in private discussions, including saying: "Do you know maybe one black country that's well run?"

Many of Nixon's comments only came to light years later, following the release of tapes from his White House years. Timothy Naftali, a presidential historian and the former director of Nixon's presidential library, said Trump's most recent comments were more jarring both because they were revealed in real time and because they came during the course of a discussion about the laws governing who can gain entry into the United States.

"This is not an example of a leak that shows the president to be a jerk," Naftali said. "This shows the president is using language that implies he's thinking like a racist while making immigration policy."

Notably, the White House did not deny Trump's comments and instead endorsed the spirit of what he appeared to be saying. In a statement, White House spokesman Raj Shah said Trump is "fighting for permanent solutions that make our country stronger by welcoming those who can contribute to our society, grow our economy and assimilate into our great nation".

Two of the Republican lawmakers who participated in the meeting, senators Tom Cotton of Arkansas and David Perdue of Georgia, said they "do not recall" Trump's derogatory comments about Africa. Another GOP attendee, South Carolina Senator Lindsay Graham, suggested the reported remarks were accurate: "Following comments by the president, I said my piece directly to him."

Trump's political allies have been through this dance before, grappling with how to position themselves after a president whose supporters they covet stakes out controversial positions. In August, after the president said "both sides" were to blame in clashes between white supremacists and counterprotesters in Charlottesville, Virginia, many GOP officials condemned Trump's remarks but maintained their overall support for his presidency.

On Friday, several black supporters and advisers to Trump vouched for his commitment to the black community after a White House event honouring Martin Luther King Junior. Paris Dennard, a senior director of strategic communications at the Thurgood Marshall College Fund, said Trump "understands this community".

GETTY IMAGES After the conversation was leaked, Trump denied he made the comments, but admitted tough language was used.

"He wants to help our community."

But the participants pointedly did not address Trump's vulgar comments. And other Trump backers made clear they wanted to steer clear of questions about whether the president is a racist.

"That's not something I want to talk about," former House Speaker Newt Gingrich said.

In Atlanta, at the congregation once led by King, the Reverend Raphael Warnock of Ebenezer Baptist Church and other faith leaders planned a news conference to condemn Trump's "vile and racist" remarks made on the eve of the Martin Luther King Jr. holiday weekend.

Warnock said it's hypocritical for Trump to sign a proclamation honouring King, given his comments.

"A giant of a man does not need a proclamation from a small man like Donald Trump," Warnock said.﻿