Armed groups fighting the U.S.-led occupation in Iraq are holding hostages in clear violation of the laws of war, Human Rights Watch said today. Human Rights Watch also said that reports of heavy civilian casualties in Falluja last week require investigation.

At least 13 and perhaps as many as 40 non-Iraqis have been abducted over the past week. Most if not all of those seized were civilians working for foreign firms and media. The abductors of 4 Italians and 3 Japanese threatened to kill their hostages unless those governments withdraw their forces from Iraq. On Wednesday, Fabrizio Quattrocchi, one of the Italian captives, was executed. The 3 Japanese were released on Thursday.

“Taking and holding hostages violates the core of international humanitarian law,” said Joe Stork, acting executive director of Human Rights Watch’s Middle East and North Africa division. “The killers of Fabrizio Quattrochi should be brought to justice and all those holding individuals for purposes of political extortion should free them immediately and unconditionally.”

Human Rights Watch also expressed grave concern at reports of heavy civilian casualties as a result of U.S. military operations in Falluja, a city of 200,000 west of Baghdad. U.S. Marines entered the city on April 6, in part to apprehend those responsible for the ambush, murder, and mutilation of four U.S. private security firm employees on March 31.

A shaky truce has been in place since April 12, after the head of the U.S.-led Coalition Provisional Authority, Paul Bremer, called for a cease fire to allow in humanitarian supplies and to “allow residents of Falluja to tend to wounded and dead.” U.S. troops reportedly used loudspeakers to announce that women, children, and elderly could leave the city, but not “military age men.” Subsequent reports however indicate that men have been among the thousands who have fled, mainly to Baghdad.

The number of killed and wounded is sharply disputed. The director of Falluja’s general hospital, Rafa al-Issawi, reportedly estimated that some 600 persons had been killed, citing reports from clinics in the city and several soccer fields where bodies were being interred. News correspondents reported seeing rows of freshly dug graves at one of the soccer fields and Khalaf al-Jumaili, a volunteer gravedigger, told the Associated Press that more than 300 persons had been buried there.

Al-Issawi, the hospital director, also said that many of the dead were women, children, and the elderly. U.S. military officials have insisted that U.S. forces have taken great precaution to avoid harming civilians and civilian casualties have been minimal.

U.S. Marine Lt. Col. Brennan Byrne, responding to the reports, said, “What I think you’ll find is 95 percent of those were military age males that were killed in the fighting. The marines are trained to be very precise in their firepower…. The fact that there are 600 [killed] goes back to the fact that the marines are very good at what they do.”

“Reports of hundreds of civilian casualties in Falluja are unconfirmed, but serious enough to warrant further inquiry,” Stork said. “At this point we just don’t know the numbers or if their deaths were the result of any unlawful behavior on the part of U.S. troops. That’s why an impartial and comprehensive investigation is in order.”

Human Rights Watch said that all parties to the conflict have a duty not to subject civilians unnecessarily to the dangers of military operations.