Newt Gingrich criticized Mitt Romney during the Facebook/NBC debate on Sunday morning over ads run by a super-PAC supporting the former Massachusetts governor.

The former House Speaker refused to recant his accusations that Romney is lying about his ties to the organization behind the ads when asked by moderator David Gregory.

"Governor, I wish you would calmly and directly state it is your former staff running the PAC. It is your millionaire friends giving to the PAC and you know some of the ads aren't true," Gingrich said.

"Of course it's former staff of mine and of course they're people who support me. They wouldn't be putting money into a PAC that supports me if they weren't people who support me," replied Romney, adding he hasn't seen the ads. "As you know, under the law, I can't direct their ads. If there's anything in there that's wrong I hope they take it out."

But Romney then noted that "the ad I saw" with Gingrich and former Speaker Nancy Pelosi (D-Calif.) to argue for a climate change bill.

Gingrich refused to back off suggestions that Romney's former firm Bain Capital had engaged in predatory behavior, shuttering businesses and laying off workers.

He said he's happy that Romney has finally expressed opposition to the mistakes weeks later, and that he hopes an upcoming 27-minute film set to be released about Bain Capital and Romney’s role there, based on mainstream newspaper accounts, is similarly accurate.

Gingrich has repeatedly blasted the super-PAC-funded ads as dishonest and called on Romney to disavow them or ask his supporters to stop airing them. Gingrich has admitted the barrage of advertisements have taken their toll on his candidacy, which has seen his poll numbers drop after briefly holding co-front-runner status in several national polls.