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GRAND JUNCTION, Colo. - Mitt Romney said there is "nothing hidden" in his tax returns that have yet to be released, responding to a question during a radio interview set to air later today regarding an onslaught of criticism from Democrats - including President Obama - on his refusal to be more transparent with his financial records.

"I don't manage them. I don't even know where they are," said Romney in an interview with Iowa Radio. "That trustee follows all U.S. laws. All the taxes are paid, as appropriate."

"All of them have been reported to the government," said Romney, adding, "There's nothing hidden there."

"If, for instance, you own shares in Renault or Fiat, you still have to disclose that in the United States," Romney said. "So, you know, I understand the president's going to try to do anything he can to divert attention from the fact that his jobs record is weak and he has no plan to make things better."

Democrats have not let up in their requests that Romney release several more of his tax returns following a Vanity Fair investigation of his offshore accounts. In January, after similarly intense criticism during the GOP primary, Romney released his 2010 tax returns as well as his estimates for his 2011 filings. Just a few months later, in April, the campaign announced that Romney had filed for an extension for his 2011 taxes and that they would be released sometime in the next six months - and definitely before the election this fall.

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The criticism intensified Monday when President Obama told ABC's New Hampshire affiliate WMUR that he too would like Romney to be more transparent.

"What's important is if you are running for president is that the American people know who you are and what you've done and that you're an open book. And that's been true of every presidential candidate dating all the way back to Mitt Romney's father," said Obama.

"Obviously there are unpleasant aspects of being poked and probed, and I understand that," Obama said. "But it's important for you to say here's who I am, and here's how I've done."