BOSTON — President Barack Obama’s re-election campaign kept up pressure against Republican rival Mitt Romney on two fronts Friday, launching a new ad defending Obama’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.

Separately, a Democratic super PAC supporting Obama released a new ad Friday arguing that Romney would only pay 1 percent in taxes under a budget plan proposed by his running mate, Wisconsin Rep. Paul Ryan. The ad’s tag line says: “Romney and Ryan. If they win, the middle class loses.” It was airing in Colorado, Florida, Ohio, Iowa, Pennsylvania and Virginia.

On a lower profile campaign day for Obama and Romney, Ryan worked for votes in Virginia, telling a cheering crowd that he is fond of hunting and fishing in the state. Both campaigns see Virginia as a bellwether; Obama won the state in 2008, the first Democrat since Lyndon B. Johnson to gain victory in Virginia.

“This is a state that has it all, and this is a state that will determine it all,” Ryan said in Glen Allen, outside Richmond.

He made no mention of Medicare, the issue that has dominated debate much of the week, driven in part by Ryan’s blueprint for overhauling the program.

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.

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.

This comes while Romney is campaigning in Alabama, South Carolina, Massachusetts and New York. He plans visits next week to Texas, Louisiana and New Mexico. None of these states is being seriously contested in the presidential race.

To be sure, Obama attends numerous fundraisers of his own. And Romney has spent significant time at public campaign events in swing states, and he will do so many times again before the Nov. 6 election.

But the amount of time Romney is devoting to private fundraisers in noncompetitive states is notable. Even when he is in swing states, he sometimes attends only a fundraiser, without mingling with non-donors or appearing before local TV cameras, as he did Wednesday in Charlotte, N.C.

Romney is pouring time into fundraisers even though he has outdistanced Obama on that front for months. The former Massachusetts governor reported raising more than $101 million along with the Republican National Committee in July. Obama’s campaign and Democratic National Committee raised $75 million for the month.

Romney’s money advantage is expanded by technically independent groups flooding airwaves with ads criticizing Obama. Two pro-GOP super PACS — Restore Our Future and American Crossroads — have raised more than $122 million since the beginning of last year. Democratic-leaning groups Priorities USA Action and American Bridge 21st Century have raised about $30 million in that time.

The candidate with the most money and TV ads doesn’t necessarily win elections, and most polls suggest Obama holds a slight lead among voters. For now, at least, Romney’s team has decided that pouring much of his time into fundraising is more valuable than another quick visit to Colorado, Florida or the other eight or 10 competitive states.

Romney, who made millions of dollars heading the private equity firm Bain Capital, is skilled at extracting money from supporters.

His Wednesday midday event in Charlotte drew more than 100 people who paid between $2,500 and $50,000 each, netting his campaign about $1.5 million. That night, a somewhat larger crowd at a swank club overlooking Birmingham, Ala., generated more than $2 million, campaign aides said.

A midday event Thursday in Greenville produced $1.7 million, and Romney held other fundraisers Thursday night in Boston. He has similar events scheduled this weekend and for much of next week.

The strategy is keeping him away from public events in competitive states for five straight days, barring a change in plans this weekend. He made a major speech in Ohio on Tuesday before diving into a long string of fundraisers in various states.

Romney managed to stay in the news this week by taking reporters’ questions Thursday in South Carolina, where he was pressed about his personal tax returns. Like Obama, he often grants interviews, by satellite, to local TV stations in swing states.

Next stop? A fundraiser Friday at the Sebonack Golf Club in Southampton, N.Y.