WASHINGTON (Reuters) - Republican presidential candidate Mitt Romney faced new questions on Thursday over whether he worked for Bain Capital longer than he previously claimed, prompting denials from the campaign and criticism from President Barack Obama's campaign.

Romney, who made a fortune as a private equity executive at Bain, has said he left the firm in 1999, when he was tapped to lead the then-troubled Salt Lake City Olympics. But the Boston Globe reported on Thursday that public records indicate he was still registered as a top official at Bain for three more years.

The issue of timing is important because Romney has said he left Bain in 1999 and thus was not responsible for bankruptcies and layoffs at Bain-owned businesses after that time.

Citing Securities and Exchange Commission (SEC) documents, the newspaper said Romney remained Bain's "sole stockholder, chairman of the board, chief executive officer and president" until 2002, when he and the firm finalized a severance deal.

Romney says he gave up day-to-day control of Bain in 1999. He has continued to earn money from his Bain investments since the severance deal expired; a disclosure form filed recently revealed roughly $2 million in new Bain income.

Romney has not revealed details about his severance agreement with Bain, raising questions about his continued ties to the firm.

The Globe cited a financial disclosure form that the former Massachusetts governor filed in 2003 that said he still owned 100 percent of Bain Capital in 2002.

Bain Capital has said Romney left the company in February 1999 and had "absolutely no involvement" with the management or investment activities of the firm since the day he left.

"Due to the sudden nature of Mr. Romney's departure, he remained the sole stockholder for a time while formal ownership was being documented and transferred to the group of partners who took over management of the firm in 1999," Bain said in a statement. "Accordingly, Mr. Romney was reported in various capacities on SEC filings during this period."

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"The article is not accurate," Romney spokeswoman Andrea Saul said of the report.

"As Bain Capital has said, as Governor Romney has said, and as has been confirmed by independent fact checkers multiple times, Governor Romney left Bain Capital in February of 1999 to run the Olympics and had no input on investments or management of companies after that point."

Democratic President Barack Obama's campaign, which has called on Romney to release more details of his fortune - which is estimated at up to $250 million - seized on the report to raise more questions about Romney's wealth and his role at Bain.

On a conference call with reporters, the Obama campaign's general counsel, Bob Bauer, raised the possibility of legal consequences for Romney if the Republican declared falsely to the SEC that he was an executive at Bain when he was not.

"It's hard to imagine that Mitt Romney - a lawyer - described as somebody who is meticulous about paperwork and scrupulous in his attention to his business was prepared to delegate to some level of sloppiness the filings he made with the Securities and Exchange Commission," said Bauer.

"If in fact, he now claims that he was in fact not ... the controlling person that is described here, that means that these statements are false. And as I said, there are very serious legal consequences that would follow."

Obama's deputy campaign manager, Stephanie Cutter, said that if Romney misrepresented his position at Bain to the SEC, it could be a felony.

"Or, he was misrepresenting his position at Bain to the American people to avoid responsibility for some of the consequences of his investments," Cutter said. "And if that's the case ... he was lying to the American people."

Cutter's "felony" comment sparked a rebuke from Romney campaign manager Matt Rhoades, who said the Obama campaign had hit a "new low" with the comment.

"President Obama ought to apologize for the out-of-control behavior of his staff, which demeans the office he holds," Rhoades said. "Campaigns are supposed to be hard fought, but statements like those made by Stephanie Cutter belittle the process and the candidate on whose behalf she works."

(Additional reporting by Jeff Mason; Editing by David Lindsey and Cynthia Osterman)