With Washington set to send billions of dollars in fresh aid to Afghanistan despite the military drawdown, the U.S. official in charge of auditing assistance programs says "it's not too late" to address the fraud and mismanagement that has bedeviled the 14-year effort to rebuild the country.

The military intervention launched after the Sept. 11 attacks has cost the United States $1 trillion, including some $110 billion in aid aimed at rebuilding one of the poorest, most violent and most corrupt countries on earth. To this day Afghanistan relies on foreign aid as it battles an increasingly potent Taliban insurgency.

But John Sopko, who has spent more than three years probing U.S.-funded projects as the special investigator general for Afghanistan reconstruction (SIGAR), said the U.S. government is partly to blame for the misused funds.

"What I'm identifying are not just Afghan or Afghan-related problems, they are problems with the way the United States government operates," he said.

He said the Pentagon and the U.S. Agency for International Development suffer from corruption as well as poor planning, oversight and accountability. He said they often fail to coordinate with one another or measure programs' effectiveness.

In October, SIGAR reported on a compressed natural gas filling station in Afghanistan's far north that cost $43 million to build but has never been used because there is no demand for the fuel. A similar station built in neighboring Pakistan would have cost a little over $300,000, SIGAR said.

It said the Pentagon was unable to explain how the Afghan plant "produced no discernible macroeconomic gains and a discounted net loss of $31 million."

In May, Sopko wrote to Secretary of Defense Ash Carter about the building of a $36 million warehouse in the main Marine Corps base in Afghanistan. The warehouse was never used for anything, he said.

Other programs have suffered from outright fraud. In September, SIGAR reported that one current and three former U.S. soldiers had been sentenced to four to eight years in prison by a North Carolina court for their involvement in a bribery scheme in southern Kandahar province that resulted in the theft of more than $10 million worth of fuel.

Since it was created in 2008, SIGAR has identified more than $1 billion in potential savings to U.S. taxpayers and published hundreds of reports, including 50 audits of reconstruction projects.

"The money that's been wasted has been wasted," Sopko said. "But we have still got $10 billion that has been authorized, appropriated but not yet spent. And we're probably going to put in $6 billion to $10 billion a year, for years to come — because if we don't, the Afghan government will collapse."

The intensifying war with the Taliban and the withdrawal of aid groups and investors has devastated Afghanistan's economy and sent unemployment soaring to 24 percent. Officials say unemployed youth are increasingly joining the insurgency out of economic desperation, helping the Taliban to expand its footprint across the country.

U.S. personnel are increasingly holed up in embassies, making it difficult to visit project sites. Tours last 6-12 months, so there's little continuity or institutional memory.

"People have to realize that you can't do diplomacy in an environment like this without some risk, and we are becoming more and more risk-averse," Sopko said. "We cannot continue to do diplomacy with this totally 100-percent risk-free mentality because we are going to lose."

Sopko said it's time to "hit the reset button and take a look at what worked and what didn't work."

The biggest failure of the reconstruction effort, he said, was the outlay of nearly $8 billion since 2001 to eradicate poppies, the main ingredient in heroin and Afghanistan's chief export. The crop is worth some $3 billion a year and is a key source of income for the Taliban.

"It's the gorilla in the room we just want to ignore, but that gorilla will eat this room," Sopko said.

SIGAR found last year that the U.S. had spent $7.6 billion on counter-narcotics efforts in Afghanistan since 2001. Opium production has dropped by 50 percent this year, not because of eradication efforts, but because of drought, pests and other environmental factors, Sopko said.

"Any metrics you give — price, purity, addiction rates, production — the only improvements we have seen have been caused by Mother Nature," he said.