Newt Gingrich's political director in Iowa has resigned over comments he made disparaging Mitt Romney's religion.

Craig Bergman told a focus group on last Wednesday that Mormonism is a "cult" and implied it could hurt Romney in a general election against President Obama, The Iowa Republican reported.

The comment clashed with a vow Gingrich has made to avoid negative attacks during the Republican presidential primary.

"Craig Bergman agreed to step away from his role with Newt 2012 today," Gingrich spokesman R.C. Hammond said in a statement Tuesday evening. "He made a comment to a focus group prior to becoming an employee that is inconsistent with Newt 2012's pledge to run a positive and solutions orientated campaign."

Bergman joined Gingrich's campaign last week, but not until after the focus group in question, according to the campaign.

Gingrich opponents have charged that he has already violated his pledge to run a positive campaign by dispatching surrogates to attack Romney on his behalf and making critical remarks about the former Massachusetts governor during debates.

The GOP hopefuls have treaded delicately around discussing other candidates' personal faith, in part due to an uproar that ensued after Robert Jeffress, a Texas pastor, called Mormonism a cult the same day he endorsed Rick Perry.