The Obama campaign is taking another tack in its ongoing effort to wrench more tax documents from Mitt Romney. 

In an unusual offer to the Romney campaign early Friday morning, Obama's top campaign official pledged to refrain from criticizing the Republican candidate's transparency on taxes if he agrees to release five more years of returns. 

Obama campaign manager Jim Messina offered to strike the deal in a letter to Romney campaign manager Matt Rhoades. It comes after Romney said a day earlier that he's "never paid less than 13 percent" in taxes over the last 10 years. 

Rhoades, pressing Romney once again for documentation, wrote that he wanted to offer "assurances" to allay Romney's concerns that releasing additional tax returns would just feed the Democrats' appetite for more. 

"So I am prepared to provide assurances on just that point: if the Governor will release