WASHINGTON (AP) - President Barack Obama says he's had to point out "sharp differences" with Mitt Romney on issues, but says nothing in his campaign ads about the GOP candidate has been "out of bounds."

At an impromptu White House news conference, Obama says his speeches have focused on substantive issues like taxes and spending. He says the ads run by his re-election organization also are "focused on the issues." By contrast, he says that Romney has aired "patently false" claims that he's "gutting" welfare's work requirement.

Obama also defends ads attacking Romney's refusal to release more than two years' worth of tax returns. He says those seeking the White House must know their life is an "open book." He says pressing Romney on this is "pretty standard stuff" and not "overly personal"