Donald Trump came under fire Sunday for declining to reject an endorsement by David Duke, a white nationalist and former Grand Wizard of the Ku Klux Klan.
The frontrunner in the race for the Republican presidential nomination said he knew nothing about Duke when asked about the matter on CNN's "State of the Union" talk show.
"I don't know what group you're talking about. You wouldn't want me to condemn a group that I know nothing about. I'd have to look," Trump said.
Last year, a technology blog unearthed a 1927 report according to which Fred Trump -- Donald Trump's father -- was one of seven men arrested during clashes between 1,000 KKK members and 100 police officers in Queens, New York.
Trump has denied that "ridiculous" report, telling the Daily Mail, a British newspaper: "He was never arrested. He has nothing to do with this. This never happened. This is nonsense and it never happened."
The Anti-Defamation League on Thursday had called on Trump to distance himself "unequivocally" from Duke and other white supremacists.
It said Duke had recently urged voters to volunteer for the Trump campaign, and quoted him as saying on his radio program: "Voting against Donald Trump at this point is really treason to your heritage."
Trump appeared surprised when asked about the issue at a news conference Friday with New Jersey Governor Chris Christie.
"David Duke endorsed me? I disavow."
His latest comments, however, were immediately criticized by other presidential candidates.
"Hate groups have no place in America. We are stronger together. End of story," Ohio Governor John Kasich tweeted.
"Really sad," said Senator Ted Cruz, another rival. "@realDonaldTrump you're better than this. We should all agree, racism is wrong, KKK is abhorrent."
And conservative media baron Rupert Murdoch urged Republicans to "cool it."
"Both 'establishment' Republicans and Trump need to cool it and close ranks to fight real enemy. Trump, Rubio, Kasich could all win general," he tweeted.
Bernie Sanders, who is running for the Democratic nomination against Hillary Clinton, also weighed in.
"America's first black president cannot and will not be succeeded by a hatemonger who refuses to condemn the KKK," he wrote.
In a rare sign of agreement on a common cause between the two Democratic rivals, Clinton retweeted Sanders's comment.
Trump's latest remarks on the subject come just a day after another Klan brawl, this time in Anaheim, California.
Three people were stabbed, one of them critically, and 13 were arrested after a Klan rally devolved into clashes with counterprotesters.