Barack Obama has led politicians, sports stars and other public figures in condemning racist comments attributed to the Los Angeles Clippers owner Donald Sterling, a barrage of condemnation likely to increase with the leaking of apparently additional remarks.

On Sunday morning, the US sports news site Deadspin posted what it said was an extended, 15-minute version of the conversation.

The president said the comments allegedly made by the basketball tycoon were “incredibly offensive” and showed how the United States continued to wrestle with the legacy of race, slavery and segregation.

"When ignorant folks want to advertise their ignorance, you don't really have to do anything, you just let them talk. That's what happened here," he told a press conference in Malaysia, the penultimate stop of an Asia tour.

Political unity over issue
In a rare display of bipartisan unity, Republicans joined Obama, rap stars, athletes and others in lambasting Sterling, 80, who has owned the Clippers, a National Basketball Association (NBA) franchise, for nearly three decades.

The NBA opened an investigation and the National Association for the Advancement of Coloured People said it would not give Sterling a lifetime achievement award which he had been scheduled to receive next month. The NAACP honoured him in 2009 despite accusations of racism in a lawsuit brought then by the team's former general manager, Elgin Baylor.

Sterling became a national pariah over the weekend after the news site TMZ posted a 10-minute recording of what it said was a 9 April conversation he had with his girlfriend, Vanessa Stiviano, 38.

"It bothers me a lot that you want to broadcast that you're associating with black people,” the man identified as Sterling says at one point in the recording, scolding the woman for posting photos of herself with black people.

“I'm just saying, in your … Instagrams, you don't have to have yourself with, walking with black people.”

Magic Johnson responds
Magic Johnson, who used to play for the Los Angeles Lakers and is in the NBA Hall of Fame, used Twitter to say: "I will never go to a Clippers game again as long as Donald Sterling is the owner.”

Johnson also lamented "a black eye for the NBA" and said he felt bad that friends such as Clippers coach Doc Rivers and point guard Chris Paul had to work for Sterling. The former Clippers guard Baron Davis tweeted that Sterling's discrimination had been "going on for a long time".

Clippers say views are not the owners
As the comments continued to go viral on Sunday the Clippers president, Andy Roeser, said in a statement the team did not know if the voice belonged to Sterling but that the comments did not reflect the owner's views.

"Mr Sterling is emphatic that what is reflected on that recording is not consistent with, nor does it reflect his views, beliefs or feelings,” the statement said.

“It is the antithesis of who he is, what he believes and how he has lived his life. He feels terrible that such sentiments are being attributed to him and apologises to anyone who might have been hurt by them."

The outcry looked set to grow, however, after Deadspin posted its version of the conversation.

At one point the voice attributed to Stiviano – who is of black and Mexican descent – challenges her interlocutor over the fact most of his players are black.

Denying he is a racist, the male voice replies: “I support them and give them food, and clothes, and cars and houses. Who gives it to them? Does someone else give it to them?”

The man said to be Sterling appears placated by the woman's meeting Matt Kemp, a baseball star, when she says he is of mixed race, “lighter and whiter” than she is.

He then suggests racism against blacks is a global reality and cannot be changed: “It's the world. You go to Israel, the blacks are just treated like dogs.”

Asked if black Jews were apparently worth less than white Jews, the male voice says: “100%, 50, 100%.”

NBA promises investigation
The NBA commissioner, Adam Silver, promised that an “extraordinarily” swift investigation would confirm the authenticity of the recording and that he would interview both Sterling and the woman in the recording.

"We do hope to have this wrapped up in the next few days," he said.

In Malaysia Obama, speaking at a press conference alongside Malaysian prime minister Najib Razak, said vestiges of discrimination endured in the US. “We've made enormous strides, but you're going to continue to see this percolate up every so often,” he said.

The president urged the NBA to “do the right thing”.

Senator Bob Corker, a Republican from Tennessee, echoed the president. “It's just outrageous that in 2014 comments like these are being made,” he said. “The president's remarks were appropriate.”

Even before the Sterling furore, racism had landed back on the political agenda. Republicans who had supported Nevada rancher Cliven Bundy in his recent face-off with federal authorities condemned him after he said black people might be “better off as slaves, picking cotton”.

Days earlier, the supreme court upheld a ban on affirmative action policies that favour minority students, a ruling that racial equality campaigners called a significant setback for the civil rights movement.