Obama ad: Romney tax plan hurts middle class

"Mitt Romney, he won't reveal what's in his taxes and he won't tell you what he'd do to yours," a narrator says in the ad.

"To pay for huge new tax breaks for millionaires like him, Romney would have to raise taxes on the middle class," the ad continues, adding that taxes could increase by $2,000 per middle class family and that the tax increases could come from the loss of home mortgage reduction, health care credits and college tuition breaks.

"How much would you pay? Romney just won't say," the ad concludes.

The spot, which will air in the battleground states of Iowa, Nevada, Virginia and Ohio, comes as Mitt Romney has come under pressure, including from conservatives in his own party, to reveal more details of his policy proposals.

Romney and his running mate Paul Ryan have repeatedly said that to make up for the loss of revenue from lowering taxes, he would eliminate loopholes and deductions for high-income earners, but he has not specified which deductions he would get rid of. In the absence of those details, Democrats have jumped on several independent studies, including one by the Tax Policy Center, that suggest middle-class Americans would be negatively impacted from the elimination of all deductions, including charitable and mortgage deductions.