Afghan National Army (ANA) soldiers march as they participate in a combat training exercise at the Afghan National Military training centre (KMTC) in Kabul on October 22, 2014.

The Pentagon wasted as much as $28 million over the past decade buying uniforms for the Afghan army with a woodland camouflage pattern appropriate for a tiny fraction of that war-torn country, according to the Special Inspector General for Afghanistan Reconstruction.

The Afghan Defense Minister picked the pricey, privately owned "forest" color pattern over free camouflage schemes owned by the U.S. government, according to an advance copy of the report due out on Wednesday. The scathing, 17-page study notes that "forests cover only 2.1% of Afghanistan's total land area."

"My concern is what if the minister of defense liked purple, or liked pink?" John Sopko, the special inspector general, told USA TODAY in an interview. "Are we going to buy pink uniforms for soldiers and not ask questions? That's insane. This is just simply stupid on its face. We wasted $28 million of taxpayers' money in the name of fashion, because the defense minister thought that that pattern was pretty. So if he thought pink or chartreuse was it, would we have done that?"

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For years, Sopko's office has scalded the Pentagon for squandering tens of millions of dollars of the $66 billion Congress has appropriated to train, equip and house Afghan security forces. Wednesday's installment on uniforms was particularly pungent, noting that special tailoring — zippers instead of buttons — boosted the cost of uniforms of already dubious value.

The report's release comes as Defense Secretary Jim Mattis considers sending thousands more U.S. troops to bolster beleaguered Afghan forces in what has become America's longest war. Afghan troops face a resurgent Taliban insurgency, an offshoot of the Islamic State (ISIS), and other terrorist groups.

The Pentagon has spent $93 million on the uniforms since 2007. Switching to a camouflage pattern owned by the U.S. military could save taxpayers as much as $71 million over the next decade, the inspector general found.

The Pentagon, in its written response, didn't quibble with the findings. Instead, in a letter to Sopko, the military acknowledged the need for a cost-benefit analysis "to determine whether there is a more effective alternative, considering both operational environment and cost."