Mr Obama (2nd r) was asked about the plight of auto workers
Barack Obama, candidate for the Democratic Party's nomination to run for US president, has apologised to a reporter for calling her "sweetie".
Reporter Peggy Agar, of the WXYZ television network in Michigan, had shouted a question as Mr Obama toured a Chrysler car plant in Detroit.
Mr Obama said: "Hold on one second, sweetie" and did not answer.
He later left a message for Ms Agar saying it was a "bad habit" and he "meant no disrespect".
Ms Agar told the Detroit News: "I've been called worse."
Mr Obama has been in Michigan to bolster his campaign as his battle for the Democratic nomination with rival Hillary Clinton reaches its climax.
During his visit he has secured the endorsement of former US Democratic presidential contender, John Edwards.
The 'sweetie' incident and Barack Obama's apology
On his trip to the Chrysler LLC plant, Ms Agar shouted out: "How are you going to help the American auto workers?"
Mr Obama said: "Hold on one second, sweetie, we'll do a press [session], thanks."
The Illinois senator later left a phone message that was played on the television station.
In it he said: "That's a bad habit of mine. I do it sometimes with all kinds of people. I mean no disrespect and so I am duly chastened on that front.
"Feel free to call me back. I expect that my press team will be happy to try to make it up to you whenever we are in Detroit next."
It was the second time Mr Obama had been caught with the word - he used it referring to a factory worker in Pennsylvania in April.
Ms Agar said the apology surprised her but she was more concerned he had not answered her question.
"People in Michigan have to make a decision about who they're going to vote for... [Mr Obama] could take a second to say what he's going to do for them."