Trump tweeted a convoluted denial early Friday but Democratic Senator Dick Durbin pushed back, saying the president had repeatedly used such "vile, racist" language during a meeting with lawmakers in search of a delicate compromise on immigration reform.
"The language used by me at the DACA meeting was tough, but this was not the language used," Trump said, apparently referring to the remarks quoted by The Washington Post and The New York Times.
Thursday's White House meeting was held to discuss a bipartisan deal that would limit immigrants from bringing family members into the country, and restrict the green card visa lottery, in exchange for shielding hundreds of thousands of young people known as "Dreamers" from deportation.
After lawmakers raised the issue of protections for immigrants from African nations, Haiti and El Salvador, the president reportedly demanded to know why the United States should accept immigrants from "shithole countries," rather than -- for instance -- wealthy and overwhelmingly white Norway.
Durbin said that Trump specifically asked, "Do we need more Haitians?," before launching into a diatribe about African immigration.
Trump then "said things which were hate-filled, vile and racist," Durbin said, adding that "shithole" was "the exact word used by the president, not just once but repeatedly."
Trump specifically denied he ever said "anything derogatory" about the people of Haiti.
I have a wonderful relationship with Haitians!" he tweeted.
But the government of Haiti -- which Friday marked eight years since it was hit by a devastating earthquake that killed at least 200,000 people -- declared itself "outraged and shocked" by the "racist" slur.
Trump's reported comments drew similar protests from the 55-nation African Union, which called them "clearly" racist, while El Salvador slammed a "deplorable" slur, and the southern African state of Botswana hauled in the US ambassador to complain.
At the United Nations, rights office spokesman Rupert Colville called them "shocking and shameful."
"Sorry, but there is no other word one can use but 'racist'," he told reporters. "You cannot dismiss entire countries and continents as 'shitholes' whose entire populations, who are not white, are therefore not welcome."
The State Department was left scrambling to contain the damage, with a top official saying that -- while Trump denies using the language attributed to him -- envoys had been briefed to convey Washington's respect if summoned to explain themselves.
The US president and lawmakers are currently in search of a bipartisan compromise on immigration, involving intense negotiations about how to shield from deportation nearly 800,000 so-called "Dreamers," who came to the United States illegally as children.
Last year, Trump scrapped the Obama-era Deferred Action for Childhood Arrivals (DACA) program that protected the immigrants, and set a deadline of March 5 for Congress to legislate a fix.
The reported "shithole" comment triggered a firestorm of criticism from both Democrats and Republicans.
"It's not how a president should speak. It's not how a president should behave. Most of all, it's not what a president should believe," tweeted the Democratic former vice president Joe Biden.
"We're better than this," he added.
Trump's Republicans were also plainly unhappy, with House Speaker Paul Ryan describing the reported comments as "very unfortunate" and "unhelpful."
Mia Love, a congresswoman from Utah who is of Haitian descent, called them "unkind" and "divisive" while South Carolina's Tim Scott, the only black Republican senator, said if Trump really did use those words, it would be "disappointing."
In an oddly-timed coincidence, the US president on Friday signed a declaration honoring the civil rights icon Martin Luther King Jr, three days before the federal holiday celebrated in his honor.
Ignoring shouted questions about the mounting firestorm over race, the president paid tribute during a brief ceremony to the reverend's "peaceful crusade for justice and equality."
Nevertheless, the uproar has revived attention on previous remarks by Trump that have ignited accusations of racism.
Trump earned national political prominence by promoting the falsehood that Barack Obama, America's first African-American president, was not born in the United States.
He has characterized Mexican immigrants as "rapists," repeatedly questioned the loyalty of Muslim immigrants, denounced NFL players for kneeling during the national anthem in protest at police brutality against African Americans, and made questionable comments about a violent white supremacist rally.
The White House was also forced to deny a previous New York Times report that Trump said in a June meeting on immigration that Haitians "all have AIDS."
Democratic congressman Luis Gutierrez put his criticism bluntly: "We can now say with 100% confidence that the president is a racist who does not share the values enshrined in our Constitution."