Iraqi troops have found "hostage slaughterhouses" in Fallujah (search) where foreign captives were held and killed, the commander of Iraqi forces in the city said Wednesday.

Troops found CDs and documents of people taken captive in houses in the northern part of Fallujah, Maj. Gen. Abdul Qader Mohammed Jassem Mohan told reporters.

The most notorious abductions in Iraq have been by the Al Qaeda-linked group led by Jordanian militant Abu Musab al-Zarqawi (search), who was believed to be in Fallujah but who commanders now say likely fled the city before the huge offensive launched this week by U.S. and Iraqi forces.

Mohan did not say that remains of captives were found and did not comment on whether the houses were believed linked to al-Zarqawi or any of several other militant groups that have claimed kidnappings.

"We have found hostage slaughterhouses in Fallujah that were used by these people and the black clothing that they used to wear to identify themselves, hundreds of CDs and whole records with names of hostages," the general said at a military camp near Fallujah.

Mohan was unsure if the hostage records included the names of any of the at least nine foreigners still in the hands of kidnappers — most notably, British aid worker Margaret Hassan (search), French journalists Christian Chesnot (search) and Georges Malbrunot (search) and two Americans.

"I did not look closely" at the documents, he said.

More than 170 foreigners have been kidnapped this year, and more than 30 of them have been killed by their captors.

Al-Zarqawi's followers have beheaded three Americans, two Britons, a Japanese and a South Korean, usually releasing grisly videos showing the decapitations.