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Militants strapped a pair of mentally disabled women with explosives and blew them up by remote control in two Iraqi pet bazaars, killing at least 73 people in the deadliest day since the United States began pouring extra troops into Baghdad.
Brigadier General Qassim al-Moussawi, Iraq's chief military spokesman in Baghdad, said the women had Down's syndrome and may not have known they were on a suicide mission.
The tactic would support US claims that al Qaeda in Iraq may be increasingly desperate and running short of able-bodied men willing or available for such missions.
US Ambassador to Iraq Ryan Crocker said the bombings showed that a resilient al Qaeda has "found a different, deadly way" to try to destabilise Iraq.
"There is nothing they won't do if they think it will work in creating carnage and the political fallout that comes from that," he said.
The first bomb was detonated around 10:20am local time in the central al Ghazil market. Police and hospital officials said at least 46 people were killed and more than 100 wounded.
Local police said the woman wearing the bomb sold cream in the mornings at the market and was known to locals as "the crazy lady".
The weekly pet bazaar had been bombed several times during the war, but with violence declining in the capital, the market had regained popularity as a shopping district and place to stroll on Fridays, the Muslim day of prayer.
But Friday offered a scene of carnage straight out of the worst days of the conflict.
"I have been going to the pet market with my friend every Friday, selling and buying pigeons," said Ali Ahmed, a pigeon vendor who was hit by shrapnel in his legs and chest.
"It was nice weather today and the market was so crowded."
Police and civil defence officials piled the wounded into wheelbarrows, cars and the back of pick-up trucks while US soldiers helped secure the area. Officials at nearby hospitals said they struggled to cope with the wounded.
"Most people who visit this market are poor and just want to enjoy themselves, but they came and got killed," said Hassan Salman, who sells bird seed at the Ghazil market.
The Ghazil market opens only on Fridays and sells a colourful range of creatures from guard dogs and monkeys to parrots, pigeons and tropical fish.
The combined death toll from yesterday's attacks is the deadliest for Baghdad since June 19, when a car bomb killed 87 people near a Shiite mosque.
However, violence has fallen sharply across Iraq, with the number of attacks down 60 per cent since last June.
The declining violence has been attributed to 30,000 extra US troops, which became fully deployed last June, and the growth of primarily Sunni Arab local police units.
