Reports that he had called them “shithole countries” in an Oval Office meeting generated a backlash worldwide and Mr Trump later denied them.
However Democratic Senator Dick Durbin said he heard Mr Trump use “racist” language.
The president called some African nations “shitholes”, he said.
Amid widespread coverage of his reported remarks, on Friday Mr Trump tweeted his language at the meeting “was tough, but this was not the language used”.
The Washington Post, the New York Times, Politico and the Wall Street Journal all reported the comments on Thursday, quoting witnesses or people briefed on the meeting. The White House did not deny them.
“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 yesterday,” Mr Durbin told reporters on Friday.
Mr Trump’s reported remarks came as both Republican and Democratic lawmakers visited him on Thursday to propose a deal on immigration.
Mr Trump was said to have told them that instead of granting temporary residency to citizens of countries hit by natural disasters, war or epidemics, the US should instead be taking in migrants from countries like Norway.
“Why are we having all these people from shithole countries come here?” the Washington Post quoted him as saying.
Mr Durbin said that when Mr Trump was told that the largest groups of immigrants with Temporary Protected Status (TPS) were from El Salvador, Honduras and Haiti, the president responded: “Haitians? Do we need more Haitians?”