Oops.

It's hard to think of another case where sanctions have had such drastic effects on a country's economy so quickly. Iran used to export 2.14 million barrels of oil every day; that was two years ago. Now that number stands at some 890,000. The value of the rial has crashed, and the IMF reports that Iran's economy has shrunk for the first time in more than two decades. Even Mahmoud Ahmadinejad admits the country is feeling the pressure.

But despite the U.S. campaign to marginalize Iran, a new report suggests Washington may be unwittingly undercutting its own efforts by buying up Iranian oil -- a clear violation of the sanctions prohibiting almost all economic activity with the pariah state.

Since 2007, the U.S.-led coalition in Afghanistan has allocated $1.55 billion for the purchase of fuel for the Afghan national army (ANA). Problem is, nobody seems to know for certain whether that fuel came partly from Iran.

"DOD is unable to determine if any of the $1.1 billion in fuel purchased for the ANA between fiscal year 2007 and 2012 came from Iran, in violation of U.S. economic sanctions," according to the report filed by the Special Inspector General for Afghan Reconstruction (SIGAR). "Given the Afghan government's continued challenges in overseeing and expending direct assistance funds, it will become more difficult for DOD to account for the use of U.S. funds as it begins to transfer funds -- in March 2013 -- directly to the Afghan government for the procurement and delivery of ANSF fuel."