Brig. Gen. Qassim al-Moussawi, the Iraqi military spokesman, said, "We have not seen such a wave of attacks since the security plan began. These are terrorist challenges. Ninety-five percent of those killed today were civilians."

Late Wednesday, Prime Minister Nouri al-Maliki ordered the arrest of the Iraqi army colonel who was in charge of security in the region around the Sadriyah market. The colonel's name was not given.

"Our Iraqi people are being subjected to a brutal attack that does not differentiate between an old man, a child or a woman. This targeting of civilian populations brings back to our minds the mass crimes and genocide committed by the Saddamist dictatorial regime," said a statement from al-Maliki's office.

The 127 deaths in the market bombing were recorded by Raad Muhsin, an official at al-Kindi Hospital morgue where the victims were taken. A police official confirmed the toll, speaking on condition of anonymity because he was not authorized to release the information.

Besides the market attack, bombs struck Shiite targets in the capital at a police checkpoint, near a hospital and in a small bus.

Nationwide the number of people killed or found dead was 233, which was second only to a total of 281 killed or found dead on Nov. 23, 2006. Those figures are according to AP record-keeping, which began in May 2005.

Caldwell said militants were "attempting to destroy any sense of security the people of Baghdad were beginning to feel with the security operation in Baghdad."

He called insurgents a "vicious cancer on the body of Iraq. You've got to keep fighting it. We're not going to give up."

Many of the most devastating bomb attacks in the country have come in the past several months, indicating insurgents have developed more sophisticated or powerful explosives.

U.S. military officials announced that last week they found 3,000 gallons of nitric acid hidden in a warehouse in downtown Baghdad. U.S. forces discovered the acid, a key fertilizer component that can also be used in explosives, during a routine search April 12, the military said.

Timothy M. Swager, head of the chemistry department at the Massachusetts Institute of Technology, said that aside from being used to make explosives, nitric acid could cause dangerous burns if used directly on people.

"Like all strong acids, if you sprayed people directly with it would burn them very badly," he said.

Steve Kornguth, director of the biological and chemical defense program at the University of Texas in Austin, said nitric acid is less toxic than chlorine gas at the same concentration, but could also be lethal.