President Barack Obama tried Monday to distance himself from an advertisement run by a supportive outside group suggesting there was a link between the death of a laid-off steelworker's wife and Republican Mitt Romney's former company. But Obama said he intends to keep raising sharp contrasts between himself and the GOP challenger.

"I don't think that Governor Romney was somehow responsible for the death," he said. Obama noted that the commercial "is an ad I did not approve" since it did not come from his campaign and that he had nothing to do with producing it. Furthermore, Obama said the ad "ran only once I think."

He was asked during an unscheduled appearance in the White House briefing room about the harsh tone set by some ads supporting him, especially one by the pro-Obama Super PAC Priorities USA Action.

The ad features an interview with former Kansas City steelworker Joe Soptic, who was laid off after his plant was taken over by the private equity firm cofounded by Romney, Bain Capital. The steel plant eventually filed for bankruptcy protection. The ad suggests Soptic and his wife both lost their health insurance when that happened and says that sometime later she lost a battle with cancer.

Obama said that there are "sharp differences" between himself and Romney on major issues and that those are fair game for tough ads.

Even so, nobody accused Romney "of being a felon," as some Republicans have suggested of Obama, the president said.

"If you look at the overall trajectory of our campaign, and the ads I've approved ... we point out sharp differences between candidates, but we don't go out of bounds," Obama said.

On another campaign topic, Obama condemned a GOP Senate candidate's comments on rape.

"The views expressed are offensive. Rape is rape," Obama said. He was asked about comments made on Sunday by Missouri Republican Rep. Todd Akin.

Asked in an interview Sunday on KTVI-TV if he would support abortions for women who have been raped, Akin said: "It seems to me, first of all, from what I understand from doctors, that's really rare. If it's a legitimate rape, the female body has ways to try to shut that whole thing down." Later Sunday, Akin released a statement saying that he "misspoke."

Obama said Akin's comments underscore why politicians _ a majority of whom are men _ should not make decisions on behalf of women.

Akin, who is running to unseat Missouri's Democratic Sen. Claire McCaskill, apologized further for his comments Monday and said he plans to stay in the Senate race.