Roads full of good intentions can lead to waste before reaching Hades, and the top watchdog in charge of U.S. reconstruction efforts in Afghanistan warned Tuesday that the U.S. will waste billions of dollars without better contractor oversight.

"SIGAR has a growing concern about the possible disconnect between overall U.S. policy and its field implementation," wrote John F. Sopko, Special Inspector General for Afghan Reconstruction, in his quarterly report to Congress.

"I believe the United States cannot achieve its objectives unless the execution of its policies receives at least as much attention as the intent behind them," Sopko wrote.

Sopko cited several examples of U.S. tax dollars wasted on well-intentioned but poorly executed projects, including a school at Sheberghan in Jawzjan province and a community grant project that has spent a quarter of its budget without awarding any grants.

The U.S. government's failure to reach agreement with the Afghan Ministry of Finance on illegal taxes levied on contractors has been a dangerous hindrance to reconstruction efforts as well, the report said.

At a rail crossing on the Afghan-Uzbek border, Sopko was told rail tank cars full of fuel for the U.S. military were being held illegally because of the dispute over contractor taxes. SIGAR has previously reported on contractors being arrested over the fines.

"SIGAR is well aware of the wartime environment in which contractors are operating in Afghanistan, but this can neither explain the disconnect, nor excuse the failure," Sopko said.

Another example of poor implementation is the rising cost of security services under the new Afghan Public Protection Force, the local security guards with whom the Afghan government is in the process of replacing private security contractors used by the U.S. Agency for International Development.

APPF has a monopoly on the security market, even though SIGAR investigation found officers "added little value to project security." APPF forces couldn't provide necessary services like recruiting and training new officers or supervising guards on projects, and sometimes charged for services contractors provided, according to a SIGAR report also released Tuesday and cited in the IG's quarterly report.

Despite their inability to do the work without security contractors filling in the gaps, under APPF the average cost of local guard services increased as much as 47 percent. But the U.S. Agency for International Development doesn't review those costs to make sure it is paying only for services APPF actually performed, putting the agency at risk for unrestrained security costs, according to SIGAR.

Federal agencies requested almost $11 billion for reconstruction in the 2014 budget, and the United States has promised billions more in the future.

"Much of these funds will be awarded to contractors, and unless the U.S. government improves its contract-oversight policies and practices, far too much will be wasted," Sopko said.