WASHINGTON — President Barack Obama on Monday defended the tone and focus of his re-election campaign, as he distanced himself from a controversial ad produced by a group of supporters.

The ad released by Priorities USA Action highlighted the story of steelworker laid off after Bain Capital, the private equity firm once run by Mitt Romney, bought the steel mill where he worked. The ad implied that Romney was responsible for the death of the worker's wife, who died of cancer after the worker lost his health insurance.

“I don't think Governor Romney is somehow responsible for the death of the woman that was portrayed in that ad,” Obama told reporters in a brief, unannounced news conference at the White House on Monday.

Obama was under increasing pressure to comment on the ad — and the biting tone of the campaign being run by a politician who often claims to take the high ground.

Obama stressed that the group that produced the ad is not connected to his campaign. And despite repeated airing on newscasts, the ad has not run more than once.

“Keep in mind this is an ad that I didn't approve, I did not produce, and as far as I can tell has barely run,” Obama said.

Priorities USA is a so-called super PAC — a committee able to raise cash in unlimited amounts — backing the president's bid with advertising in key states. The committee cannot coordinate with the Obama campaign, although the president has blessed its fundraising efforts.

The ad quickly caused a media stir for its damning implications and fudging of the facts. The spot does not include the fact that after the worker was laid off his wife still had her own health insurance for a year or two through her job. Nor does it note that five years passed between the closing of the mill and her death.

Former White House aide Bill Burton has defended his group, saying the spot did not imply that Romney was responsible for the woman's death.

The Obama campaign initially claimed that it had no knowledge of the man's story, although aides quickly backtracked after it was learned that the campaign had invited the man to tell his story on a conference call with reporters.

In his remarks on Monday, Obama tried to shift the focus to the Romney campaign and its advertising. He picked apart a recent attack ad that mischaracterizes Obama's policy on welfare. Obama noted the ad was being run by the Romney campaign.

“The truth of the matter is, you can't just make stuff up. That's one thing you learn as president of the United States. You get called out,” he said.

The president also defended his campaign's efforts to pressure Romney to release five years of tax returns, saying the American people expect a candidates' finances to be “an open book” in the heat of a campaign.

“And I'm not asking to, you know, disclose every detail of ... his medical records, although we normally do that as well,” Obama said.

“This isn't sort of overly personal here, guys. This is pretty standard stuff. I don't think we're being mean by asking you to do what every other presidential candidate's done, right?”

The Romney campaign said Obama “once again failed to lead” by not denouncing the third-party ad.

“President Obama's failure to stand up to dishonest rhetoric and attacks demonstrates yet again he's diminished the office that he holds and his record is nothing more than business as usual in Washington,” said campaign spokesman Ryan Williams.