No figures are available on how many Iraqi civilians, including women and children, have been killed in shootings, airstrikes and other violence involving American forces since the 2003 invasion.

However, light sentences for U.S. troops convicted of killing civilians have left some human rights groups seething. At least 16 American troops have been sentenced in such cases, according to a count by The Associated Press. Six received prison sentences of three or more years in prison. Four cases are pending.

During the Vietnam war, 95 American soldiers and 27 Marines were convicted of killing noncombatants, according to Gary D. Solis, a visiting professor of law at the U.S. Military Academy at West Point.

Last summer, Iraqi Prime Minister Ibrahim al-Jaafari complained to U.S. commanders about the "phenomenon of killing Iraqis for reasons of suspicion."

"As we say it is necessary to chase suspects, this should be done in civilized, technical and accurate ways," al-Jaafari said at the time. "We reject the killing of any of those people."

An adviser to al-Jaafari, Haider al-Abadi, said last week that the problem is U.S. troops "do not know what is going on. ... They can't differentiate between friend and foe, they don't know the language."

Al-Abadi estimated that U.S. troops have mistakenly killed thousands of Iraqis but said he believes the killings have declined because Iraqi troops are taking control of more areas. But he said the problem was serious enough for the prime minister to travel with a U.S. military escort ¡ª to protect him from other Americans.

Iraqi authorities have no jurisdiction over American and coalition forces under an agreement that the Iraqi government accepted when sovereignty was restored in 2004.

U.S. military rules give troops broad discretion to fire at perceived threats, such as vehicles that could be driven by a suicide attacker. As a result, few such shootings lead to courts-martial or harsh punishment.

"It's going to be difficult in most circumstances to reach that standard of gross negligence when you have the context of an unknown enemy, an enemy that does use civilian clothes and is often using civilian vehicles and persons to attack," said Walter Huffman, dean of the Texas Tech Law School and formerly the Army's top lawyer.

Al-Abadi, the prime minister's aide, suggested Iraqi courts should have the power to prosecute American troops for certain offenses, similar to legal arrangements that give German authorities the option of trying U.S. service members for crimes against civilians. At the least, al-Abadi said Iraqi officials should sit on U.S. military tribunals that try soldiers accused of killing Iraqis.

U.S. military law experts said such an arrangement would be highly unlikely in Iraq.

"Those status of forces agreements are only in fully developed countries with fully developed judicial systems that are very similar to ours," Huffman said.