Washington (CNN) - Signaling a shift to the next major GOP battleground, the super PAC supporting Mitt Romney, Restore Our Future, bought an additional $640,000 in television ad time in Michigan, the group confirmed to CNN Monday.
Ads from the new buy start Tuesday.
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The super PAC previously purchased $250,000 worth of commercials in Michigan, according to CNN's advertising consultant Kantar Campaign Media Analysis Group (CMAG).
Michigan, which holds its primary February 28, is setting up to be a key battleground, with rival candidate Rick Santorum vowing to fight hard there. A poll released Monday showed Santorum with a lead in the Wolverine State.
Restore Our Future is also currently up with commercials in Arizona, which votes February 28, and in Ohio, which holds its primary on March 6, Super Tuesday.
The group is expected to make buys in other Super Tuesday states soon, although officials with Restore Our Future refused to comment Monday on future plans.
All of the ads currently running from Restore Our Future are aimed at Newt Gingrich.
It is not known whether the ads in the new Michigan buy will continue hitting Gingrich or will pivot to go after Santorum.
– CNN Political Editor Paul Steinhauser contributed to this story.
You can follow Kevin Bohn on Twitter @KevinBohnCNN