It called for tighter rules on the use of contractors in a statement released with its 2006 annual report detailing human rights violations in 150 countries around the world. The rights watchdog said contracting for military detention, security and intelligence operations had fueled violations.
"We're concerned about the use of private contractors in Iraq because it creates a legal black hole of responsibility and accountability," Amnesty's Secretary-General Irene Khan told AP Television News.
"These contractors are protected from being prosecuted under Iraqi law, but they're not part of the U.S. military command. So when they commit crimes, or when they abuse human rights, they're accountable to no one."
Few aspects of the multibillion-dollar U.S. contracting effort in Iraq have been disclosed.
A report by the U.S. Government Accounting Office last year said monitoring of civilian contractors in Iraq was so poor there was no way to determine how many contractors were working on U.S.-related security and reconstruction projects or how many have been killed.
Amnesty's annual report contended the counterterrorism campaign by the United States and other powerful nations had undermined human rights around the world, draining energy and attention from crises afflicting the poor and underprivileged.
Amnesty also called for a change of strategy in Iraq, a stronger push to end rights abuses in Sudan and for closure of the Guantanamo Bay prison camp.
In Washington, State Department spokesman Sean McCormack dismissed the report, saying: "Nobody is being tortured at Guantanamo Bay."