The U.S. government paid $6.8 million for maintenance of more than 7,000 Afghan police vehicles that had been destroyed or were out of commission, according to an inspector general report released Thursday.

The report, prepared by the Special Inspector General for Afghanistan Reconstruction, cast further doubt on Afghanistan’s ability to run its nascent security forces after U.S. troops withdraw at the end of 2014.

The audit of a $350 million contract awarded to the Dubai-based firm Automotive Management Services highlights the challenges of keeping meaningful oversight of the United States’ $52 billion investment in Afghanistan’s security forces — a task that is likely to become harder as the American drawdown accelerates.

“The taxpayers and the success of our mission are at risk when contracts such as this are executed without proper planning and oversight,” SIGAR chief John F. Sopko said in a statement.

In response to the report, the NATO training mission that awarded the contract agreed to improve the mechanism it uses to track how many of the more than 30,000 vehicles donated to the Afghan police force remain operable. Late last year, after reviewing the auditors’ preliminary conclusions, the training command removed 7,324 vehicles from its maintenance roster after confirming that they had either been destroyed or had not been serviced for more than a year.

In its written response to the findings, the training command said it expects the updated tracking system to help it save as much as $5.5 million a year.

The report does not say whether investigators found evidence of willful misreporting, a common occurrence in Afghanistan, which is among the world’s most corrupt countries. It said the firm hired to service the vehicles “generally performed and billed in accordance with the contract’s terms and conditions.”

Company employees, however, sometimes did not conduct site inspections as a result of logistical challenges and security concerns, auditors found. Additional U.S. money may have been siphoned because fuel allotments for Afghan police stations are based on the number of vehicles listed on the same roster, the report said.

SIGAR issued a separate report last fall warning that the Afghan government will be unable to adequately maintain army and police facilities after 2014, when the U.S.-led military coalition is set to disband. That report warned that the United States and its allies will have to continue paying hundreds of millions of dollars to operate Afghan bases and equipment.