OTTUMWA, Iowa — Republican presidential candidate Newt Gingrich is lashing out at Mitt Romney, accusing Romney of what he calls a "negative smear campaign" fueled by a special political action committee.

Campaigning in Iowa on Tuesday, Gingrich called on Romney to demand that all ads run on his behalf by political action committees be positive.

Gingrich says the super PAC that's pouring money into spots attacking him in Iowa was created by Romney's former staff and funded by "his personal friends."

Romney has refused to disavow the ads from the super PAC called Restore Our Future, saying it would be illegal for him to coordinate with it. He tells MSNBC that such groups are a "disaster" and have made a "mockery" of the presidential campaign.