The U.S Defense Secretary Jim Mattis has criticized Pentagon officials for wasting up to $28 million to help buy uniforms for the Afghan National Army that had camouflage patterns representing lush forests, Reuters reported.

"Buying uniforms for our Afghan partners, and doing so in a way that may have wasted tens of millions of taxpayer dollars over a 10-year period, must not be seen as inconsequential in the grand scheme of the department's responsibilities and budget," Mattis said in a memo seen by Reuters news agency on July 24.

His comments refer to a report by the Special Inspector General for Afghanistan Reconstruction (SIGAR) that concluded the Pentagon needlessly spent millions to license the proprietary camouflage pattern when it already had dozens of desert patterns it could have used for free.

SIGAR, the U.S government's top watchdog on Afghanistan, said the uniform design choice was wasteful given that only 2.1 percent of Afghanistan is covered by forests.

It said it was chosen because the Afghan minister of defense at the time "liked the woodland, urban, and temperate patterns."

Mattis, in his memo, said that "cavalier or casually acquiescent decisions to spend taxpayer dollars in an ineffective and wasteful manner are not to recur."

"I expect all (Department of Defense) organizations to use this error as a catalyst to bring to light wasteful practices -- and take aggressive steps to end waste," Mattis wrote.