Democratic White House candidate Joe Biden is in damage limitation mode after saying African Americans "ain't black" if they even consider voting for President Donald Trump over him.

Gaffe-prone Mr Biden made the remark in an interview on Friday with a prominent black radio host, Charlamagne Tha God, about his outreach to black voters.

Mr Biden later expressed regret for the "cavalier" comment.

The black vote has been key to the Biden candidacy.

Throughout the 18-minute interview, Mr Biden, 77, stressed his longstanding ties to the black community, noting his overwhelming win this year in South Carolina's presidential primary, a state where the Democratic electorate is more than 60% African American.

"I won every single county. I won the largest share of the black vote that anybody had, including Barack," he said of President Barack Obama, the country's first African-American president, who picked Mr Biden as his running mate.

Mr Biden also "guaranteed" that several black women were being considered to serve as his vice-president. The presumptive nominee has already committed to selecting a woman to join him on the Democratic ticket.

Toward the end of the interview, a campaign aide interrupted to say the former vice-president was out of time.

When an aide for Mr Biden tried to end the interview, Charlamagne protested, saying: "You can't do that to black media."

"I do that to white media and black media," Mr Biden replied, adding that his wife was waiting to use their home broadcast studio.

Charlamagne urged Mr Biden to return for another interview, saying he had more questions.

"If you have a problem figuring out whether you're for me or Trump, then you ain't black," Mr Biden responded.

Charlamagne's nationally syndicated Breakfast Club show reaches more than 8 million listeners each month.