The U.S. government has spent $904 billion since 2001 on wars in Afghanistan and Iraq, and could spend more than $1.7 trillion, according to a study released Monday by the Center for Strategic and Budgetary Assessments, a nonpartisan policy research group.

The study warns that the additional burden of accrued interest payments could easily push that tab to $2.5 trillion, depending on how the cost is financed.

"In real (inflation-adjusted) terms, the [$687 billion spent] in Iraq alone has already cost more than every past U.S. war except World War II," the report notes. All figures are adjusted to use 2008 dollars.

With the $184 billion in spending for Afghanistan included, the two conflicts surpass the cost of the Vietnam War by about 50 percent, according to the report.

The total figure also includes U.S. homeland security efforts, including Operation Noble Eagle, the North American Aerospace Defense Command initiative to aid in the defense of North American skies begun Sept. 14, 2001.