BOSTON >> Barack Obama’s re-election campaign kept up pressure against Republican rival Mitt Romney on two fronts Friday, launching a new ad defending the president’s record on Medicare while challenging Romney to release at least five years of tax returns.

The TV advertisement, accusing Romney and running mate Paul Ryan of undermining the health care program critical to millions of seniors, came as Romney continued raise money in non-battleground states. That remains a top priority, even with the election less than 12 weeks away and Obama making extended visits to toss-up states such as Iowa and Ohio.

Obama campaign manager Jim Messina said the president’s camp would seek no further disclosures if Romney would release five years of his individual tax returns. The Romney campaign, which often says there will be no end to Democrats’ demands for tax records, rejected the offer.

“It is clear that President Obama wants nothing more than to talk about Gov. Romney’s tax returns instead of the issues that matter to voters,” said Romney campaign manager Matt Rhoades.

Romney released his 2010 tax return and has pledged to release his 2011 returns, but no others. Obama, like most other modern-day presidential nominees, has released several years of returns.

Obama’s campaign has questioned whether there are years when Romney paid no taxes. Romney defended his record Thursday, saying he has paid at least 13 percent of his income in federal taxes every year for the past decade.

“I did go back and look at my taxes and over the past 10 years I never paid less than 13 percent,” Romney told reporters after landing in South Carolina for a fundraising event Thursday. “I think the most recent year is 13.6 or something like that. So I paid taxes every single year.”

Aides later said Romney meant to say 13.9 percent, the amount he already disclosed for his 2010 federal return.

On average, middle-income families, those making from $50,000 to $75,000 a year, pay 12.8 percent of their income in federal taxes, according to the nonpartisan Joint Committee on Taxation.

In 2010 and 2011, Romney made about $21 million a year.

Romney is able to keep his tax rate low because most of his income is from investments, which are generally taxed at a lower rate than wages. That type of legal tax figuring is something Obama has proposed changing, although his campaign notably said nothing about Romney’s self-described tax rate itself.

In the new Medicare ad, Obama’s campaign pointed to the AARP, an organization that represents senior citizens and had said in a letter to lawmakers earlier this year that Ryan’s plan to transform Medicare into a voucher-like system would lead to higher costs for seniors.

The AARP said Obama’s approach would strengthen the program. Romney has criticized Obama for taking more than $700 billion in Medicare funds to help pay for the president’s health care law.

Obama’s campaign is running the ad in eight states: New Hampshire, Virginia, North Carolina, Florida, Ohio, Iowa, Colorado and Nevada.

The Romney campaign on Friday disputed the new ad, and repeated its claim that Obama’s plans would siphon spending from Medicare without safeguarding the program’s long-term stability.