KABUL, Afghanistan  American taxpayers have inadvertently created a network of warlords across Afghanistan who are making millions of dollars escorting NATO convoys and operating outside the control of either the Afghan government or the American and NATO militaries, according to the results of a Congressional investigation released Monday.

The investigation, begun last year by the House Subcommittee for National Security, found that money given to these Afghan warlords often amounts to little more than mafia-style protection payments, with some NATO convoys that refused to pay the warlords coming under attack.

The subcommittee, led by Representative John F. Tierney, Democrat of Massachusetts, also uncovered evidence suggesting that American taxpayer money is making its way to the Taliban. Several trucking company supervisors told investigators that they believed the gunmen they hired to escort their convoys bribed the Taliban not to attack.

The warlords who are paid with American money, the investigators said, are undermining the legitimate Afghan government that Americans soldiers and Marines are struggling to build, and will most likely threaten the government long after the Americans and NATO leave.