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President Obama, in a rare press conference Monday, disputed accusations that he’s running an unfairly negative re-election campaign – as he emerged to take questions from the White House press corps amid mounting criticism that he’s been ducking them.

The president answered a wide range of questions during the 20-minute question-and-answer session, including one about the veracity of a super PAC ad that implied Mitt Romney played a role in the death of a steelworker’s wife.

“I don’t think Governor Romney was somehow responsible for the death of that woman,” said Obama, who also made clear he didn’t approve the ad.

The call for Obama to answer questions from White House reporters in part follows a series of recent interviews he has given to such news outlets as People magazine, Entertainment Tonight and a local-radio station in which he talked about his favorite chili.

On the issue of the political uprising in Syria, Obama said the use of chemical or biological weapons by the Syrian government would be a “red line” for possible U.S. military action.

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The president also was critical about the recent comment by Rep. Todd Akin, the GOP Senate candidate in Missouri who suggested pregnancy often does not result from “legitimate rape.”

The Priorities USA Action 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 him and Romney on major issues and that those are fair game for tough ads.

Among those issues are Romney releasing two years of tax returns, said Obama. However, he took issue with a reporter question about the Obama campaign implying Romney would have committed a felony if he submitted misleading information on federal documents about his Bain tenure.

“Nobody accused Mr. Romney of being a felon,” 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."

He quickly pivoted to say a Romney campaign ad seriously mischance his position on work and welfare.

"You've got Governor Romney creating as a centerpiece of his campaign this notion that we're taking the work requirement out of welfare, which every single person here who's looked at it says is patently false," Obama said.

At issue is a recent step by the administration on welfare rules.

"In fact, what happened was that my administration -- responding to the requests of five governors, including two Republican governors -- agreed to approve giving them, those states, some flexibility in how they manage their welfare roles as long as it produced 20 percent increases in the number of people who are getting work," Obama said.

The Associated Press contributed to this report.