A U.S. government watchdog concluded Monday its military spent an "exorbitant" amount of money, nearly $43 million, on a natural gas automobile filling station in Afghanistan, for which Afghans had no use.

The Special Inspector General for Afghanistan Reconstruction said the United States undertook the project in 2011 in Sheberghan, near Afghanistan's vast natural gas fields to reduce the county's reliance on expensive imported gas.

But the watchdog concluded the U.S. Defense Department spent 140 times what it might cost to build a similar natural gas filling station in neighboring Pakistan, about $306,000.

The Inspector General said "one of the most troubling aspects of the project" is that the Pentagon "is unable to provide an explanation for the high cost of the project or to answer any other questions concerning its planning, implementation or outcome."

The report on the construction of the gas station said the cost "appears gratuitous and extreme."

The watchdog report concluded that the cost of converting gasoline-powered cars to run on natural gas, about $700 to $800, "may be prohibitive to the average Afghan" in a country where the World Bank says the average annual income is $690.

The report said that may explain why the U.S. government paid for the natural gas conversion of more than 120 Afghan cars so their drivers could use the natural gas filling station.

But the U.S. investigators said that "not surprisingly" they found no evidence that any other vehicles were converted for natural gas use.