{mosads}“Mitt Romney has put his personal financial assets in a black box and hid the key attempting to play by a different set of rules than any candidate in recent history,” Obama campaign manager Jim Messina said in a statement. “In fact, Mitt Romney’s own father released 12 years of tax returns when he ran for president. President Bush released his tax returns dating back to 1991. And President Obama released his returns dating back to 2000 when he ran for president.”

Obama’s campaign team is hoping that the issue might earn traction against Romney, much in the way that his primary opponent, Newt Gingrich, was able to gain ground in South Carolina by hammering the former governor’s refusal to release his tax returns.

“Mitt Romney has asked Americans to elect him President based on his experience as a corporate buyout specialist,” Messina’s statement continued. “Each week, new questions are raised about whether he took unusual steps to avoid paying his fair share in taxes. Today’s report suggests that Governor Romney is exploiting a loophole in order to shield his assets and investments from public review.”

But the Romney campaign points out that he has fully complied with every reporting requirement of the Office of Government Ethics, and accused the Obama campaign of trying to distract from his own record.

“President Obama will do anything to try and distract Americans from his failed record of chronic unemployment, lower incomes and higher gas prices,” said Romney spokeswoman Andrea Saul. “The Personal Financial Disclosure completely and accurately describes Governor Romney’s assets as required by the law applicable to candidates for president. If OGE had at any point considered any part of the filing insufficient, it would have made this clear.”

—Jonathan Easley contributed to this article.