Updated

The U.S. government's top auditor of spending on Afghanistan's reconstruction is warning Congress that American troop withdrawals this year and next will make it too dangerous to monitor many U.S.-funded projects.

John F. Sopko, the special inspector general for Afghan reconstruction, told the House Oversight Committee on Wednesday that $20 billion in reconstruction money has been appropriated by the Congress but not yet spent.

He said security issues and corruption in the Afghan government make it problematic that the money will be spent wisely.

Sopko said U.S. military security for civilians who oversee reconstruction projects extends only to areas where medical support is within about a 20-minute helicopter flight. As more U.S. troops leave, that so-called security "bubble" will shrink, he said, and the monitoring of projects will decline.