Donald Trump is unfamiliar with America's most notorious white supremacist organization, the Ku Klux Klan, knows nothing about the group's former Grand Wizard David Duke and backed away from condemning an endorsement from Duke or the KKK.

When he was asked if he would unequivocally condemn Duke and reject his and the KKK's support, Trump told CNN's Jake Tapper: "Just so you understand, I don't know anything about David Duke. OK? I don't know anything about what you're even talking about with white supremacy or white supremacists. So, I don't know."

He added: "I don't know, did he endorse me or what's going on, because, you know, I know nothing about David Duke. I know nothing about white supremacists. And so you're asking me a question that I'm supposed to be talking about people that I know nothing about."

Trump said there might be some "groups in there that are totally fine." When Tapper reiterated he was talking specifically about Duke and the KKK, the Republican frontrunner reiterated: "Honestly, I don't know David Duke. I don't believe I have ever met him. I'm pretty sure I didn't meet him. And I just don't know anything about him."

David Duke is well known across the US for his extreme right-wing views. He founded the Louisiana-based Knights of the Ku Klux Klan in 1974 and later left that organisation to form the National Association for the Advancement of White People.

Duke detailed his support for Trump in a Facebook post on 25 February, touting the candidate's stance against immigrants and his ability to bust up "Jewish-dominated lobbies." Duke believes Jews control the media and the US government and US Federal Reserve. The Anti-Defamation League has called on Trump to denounce Duke's support.

Oddly, Trump's comments followed his own declaration earlier in the week that he would not accept Duke's endorsement and within hours of his CNN appearance, he tweeted: "As stated at the press conference on Friday regarding David Duke — I disavow."

Clearly, Trump knows Duke, because in a statement in 2000 he called him a "Klansman," and refused to be a presidential candidate running on a ticket for the Reform Party, a new party Duke was active in at the time. He also apparently has a familial connection to a Klan incident.

Trump's father, Fred Trump, was one of seven men arrested in 1927 during a near-riot between cops and Klansmen as 1,000 white-robed members of the KKK marched through Jamaica, Queens, according to the Washington Post. The Klan marched, according to their flyer, because "native-born Protestant Americans" were being "assaulted by Roman Catholic police of New York City." It's not clear what role Fred Trump played nor was there any indication he was a member of the KKK.

When news of the arrest surfaced in 2015, Trump denied the arrest record and said it was a "completely false, ridiculous story."

GOP presidential candidate Marco Rubio immediately slammed Trump's comments on CNN.

"We cannot be the party that nominates someone who refuses to condemn white supremacists and the Ku Klux Klan," Rubio told a rally in Virginia..

"Not only is that wrong, it makes him unelectable. How are we going to grow our party with a nominee that refuses to condemn the Ku Klux Klan?" he said. "Don't tell me he doesn't know what the Ku Klux Klan is. This is serious."