The Hill reported Romney also posted a video on the Internet Friday in which he slams Gingrich for criticizing the budget plan put forth by House Budget Committee Chairman Paul Ryan of Wisconsin.
"With friends like Newt, who needs the left?" Romney's ad concludes.
In an aggressive move Thursday, Romney brought in Republican stalwarts James Talent, a former congressman and senator from Missouri, and John Sununu, a former New Hampshire governor and chief of staff to President George H.W. Bush, to attack Gingrich.
"What we're here to say -- with reluctance, but clearly -- is that he's not a reliable and trusted conservative leader," Talent said.
Sununu said the former House speaker from Georgia "is more concerned about Newt Gingrich than he is about conservative principle," The Washington Post reported.
The change of campaign strategy for Romney, a former Massachusetts governor, comes as Gingrich has forged into the lead in the polls in early caucus and primary states of Iowa, New Hampshire, South Carolina and Florida.
"The only opponent I have is Barack Obama," Gingrich said during a campaign stop in Greenville, S.C.