A House oversight subcommittee said Wednesday that it has begun a wide-ranging investigation into allegations that private security companies hired to protect Defense Department convoys in Afghanistan are paying off warlords and the Taliban to ensure safe passage.

"If shown to be true, it would mean that the United States is unintentionally engaged in a vast protection racket and, as such, may be indirectly funding the very insurgents we are trying to fight," said Rep. John F. Tierney (D-Mass.), chairman of the House oversight subcommittee on national security and foreign affairs.