Washington: US Defense Secretary Jim Mattis has issued a sharp rebuke after the Pentagon wasted millions of dollars buying the Afghan army a pricey uniform that may have made soldiers easier to spot.

According to a memo released Monday, Mattis told Pentagon procurement officials that the decision to buy the overpriced woodland green camouflage uniforms "serves as an example of a complacent mode of thinking."

"Cavalier or casually acquiescent decisions to spend taxpayer dollars in an ineffective and wasteful manner are not to recur," Mattis wrote in the July 21 memo.

The office of the Special Inspector General for Afghanistan Reconstruction (SIGAR) issued a report last month saying the Pentagon may have spent as much as $28 million more than necessary when it decided in 2007 to purchase the dark-green camouflage uniforms.

SIGAR also found that a private company held rights to the camo design and that Afghanistan´s then defense minister, Abdul Rahim Wardak, essentially chose the pattern on a whim.

The proprietary design meant the uniforms cost about 40 percent more than non-proprietary camouflage.

The highly critical SIGAR report also says officials ordered the uniforms without conducting any formal testing or evaluation.

"The purpose of equipping the Afghan National Army is to bolster the Afghan government´s capacity to provide for its own security, and ultimately, to help defend our country from terrorist attack," Mattis wrote.

He added that he wanted the episode to serve as a "catalyst" to bring to light wasteful practices.

Lawmakers at the House Armed Services Committee are scheduled to hold a hearing Tuesday on the matter.

Mattis is considering whether to send thousands more US troops to Afghanistan to help beleaguered Afghan partners as they struggle to contain a resurgent Taliban.