Presumptive US Republican presidential nominee Donald Trump has said his comments questioning the impartiality of a Mexican-American judge had been misconstrued as a broad attack on people of Mexican heritage.
Mr Trump said, however, that it was fair to question the judge's impartiality in the civil suit against Trump University and whether he could receive a fair trial.
The businessman has received widespread criticism, including from within his own party, over the remarks.
House Speaker Paul Ryan has denounced Mr Trump's comments as "the textbook definition of a racist comment".
Yesterday, Mr Trump insisted his concerns were valid.
Mr Trump's repeated insistence that US District Judge Gonzalo Curiel is biased in a case involving him because he was born to Mexican parents threatened to disrupt Republicans' already difficult efforts to unite behind the candidate.
Mr Ryan's emphatic rejection showed anxiety among party leaders about their ability to hang on to control of the US Congress in the election, if voters trounce Mr Trump and also punish Republicans lower down on the ticket.
The issue also plunged the Trump campaign into disarray as his core supporters struggled to explain his remarks amid appeals from party leaders for Mr Trump to apologise and move on.
Mr Ryan, the top elected US Republican, expressed misgivings last month about Mr Trump after the real estate developer became the party's presumptive presidential nominee, but finally gave his endorsement last week.
Mr Ryan was swarmed with reporters' questions about whether he had any remorse over the endorsement.
Mr Trump spent most of the past week denouncing Judge Curiel for keeping alive a lawsuit over Mr Trump's defunct real estate training school.
Mr Trump said the judge was biased because of his heritage.
"I regret those comments that he made. Claiming a person can't do their job because of their race is sort of like the textbook definition of a racist comment. I think that should be absolutely disavowed," Mr Ryan told reporters.
However, Mr Ryan said he still supported Mr Trump, adding a Trump presidency would be preferable to a White House occupied by Hillary Clinton
Mr Ryan's counterpart in the Senate, Mitch McConnell, said Mr Trump should stop attacking minority groups.
Meanwhile, a group has been established in Ireland to coordinate 'Trump Not Welcome' protests when Mr Trump visits the country later this month.
The group was established following a meeting attended by TDs from Anti-Austerity Alliance, People Before Profit and the Green Party, as well as activists from a number of groups.
