Romney "is going to have to answer those questions, because if he aspires to being president, one of the things you learn is you are ultimately responsible for the conduct of your operations," Obama told ABC television affiliate WJLA.

"I think that's a legitimate part of the campaign."

He said Romney should answer these questions soon, with the November 6 elections just around the corner.

The Obama campaign has seized on a Boston Globe report citing government records that appear to show the Republican remained in control of the private equity firm for three years beyond 1999, when he says he stepped down.

The date could be important, as Bain Capital is alleged to have invested in firms that moved workers overseas after that year and Obama supporters are attempting to paint Romney as a destroyer of jobs.

Romney's camp has rejected the allegations, problematic for a candidate who repeatedly cites his time at Bain as giving him private sector experience that Obama lacks to put an end to months of stubbornly high unemployment hovering above eight percent.