BAGHDAD — Remote-controlled explosives strapped to two mentally retarded women detonated in a coordinated attack on Baghdad pet bazaars Friday, Iraqi officials said, killing at least 73 people in the deadliest day since the U.S. sent 30,000 extra troops to the capital last spring.

The chief Iraqi military spokesman in Baghdad, Brig. Gen. Qassim al-Moussawi, said the female bombers had Down syndrome and that the explosives were detonated by remote control _ indicating they may not having been willing attackers in what could be a new method by suspected Sunni insurgents to subvert stepped up security measures.

Secretary of State Condoleezza Rice said the use of mentally retarded women as suicide bombers proves al-Qaida is "the most brutal and bankrupt of movements" and will strengthen Iraqi resolve to reject terrorism.

The first attack Friday occurred at about 10:20 a.m. in the central al-Ghazl market. The weekly bazaar has been bombed several times since the war started but recently had re-emerged as a popular place to shop and stroll as Baghdad security improved and a Friday ban on driving was lifted.

Four police and hospital officials said at least 46 people were killed and more than 100 wounded. Firefighters scooped up debris scattered among pools of blood, clothing and pigeon carcasses.

About 20 minutes later, a second female suicide bomber struck a bird market in a predominantly Shiite area in southeastern Baghdad. That blast killed as many as 27 people and wounded 67, according to police and hospital officials.

One witness who declined to be identified told AP Television News that the woman said she had birds to sell, then blew herself up as people gathered around to inspect them.

The attacks were the latest in a series of violent incidents that have been chipping away at Iraqi confidence in the permanence of recent security gains.

Iraqi President Jalal Talabani said about 70 people were killed in both attacks, which he said were committed by terrorists motivated by revenge and "to show that they are still able to stop the march of history and of our people toward reconciliation."

Police initially said the bomb at al-Ghazl market was hidden in a box of birds but determined it was a suicide attack after finding the woman's head, an officer said, speaking on condition of anonymity because he wasn't authorized to release the information.

Pigeon vendor Ali Ahmed, who was hit by shrapnel in his legs and chest, said he was worried about his friend who disappeared after the blast about 40 yards away.

"I just remember the horrible scene of the bodies of dead and wounded people mixed with the blood of animals and birds, then I found myself lying in a hospital bed," he said.

Navy Cmdr. Scott Rye, a U.S. military spokesman, gave lower casualty figures, saying seven were killed and 23 wounded in the first bombing, and 20 killed and 30 wounded in the second. He confirmed both attacks were carried out by women wearing explosives vests and said the attacks appeared to be coordinated and likely the work of al-Qaida in Iraq.

Associated Press records show that since the start of the war at least 151 people have been killed in at least 17 attacks or attempted attacks by female suicide bombers, including today's bombings.

The most recent was on Jan. 16 when a female suicide bomber detonated her explosives as Shiites were preparing for a ceremony marking the holiday of Ashoura in a Shiite village near the Diyala provincial capital of Baqouba.

Involving women in fighting violates cultural taboos in Iraq, but the U.S. military has warned that al-Qaida in Iraq is recruiting females and youths to stage suicide attacks because militants are increasingly desperate to thwart stepped-up security measures.

Women in Iraq often wear a black Islamic robe known as an abaya and can avoid thorough searches at checkpoints because men are not allowed to search them and there's a dearth of female guards.

In January 2005, Iraq's interior minister said that insurgents used a disabled child as one of the suicide bombers who launched attacks on election day. Police at the scene of the bombing said the child appeared to have Down syndrome.

A bomb hidden in a box of small birds also exploded at the al-Ghazl market in late November, killing at least 15 people and wounding dozens. The U.S. military blamed the November attack on Iranian-backed Shiite militants, saying they had hoped al-Qaida in Iraq would be held responsible for the attack so Iraqis would turn to them for protection.

The U.S. military has been unable to stop the suicide bombings despite a steep drop in violence in the past six months, but the explosions on Friday were the deadliest in the capital since Aug. 1, when some 70 people were killed in three attacks, including 50 in a fuel truck explosion in Baghdad.

Rae Muhsin, the 21-year-old owner of a cell phone store, said he was walking toward the New Baghdad bird market in southeastern Baghdad when the blast occurred, shattering the windows of nearby stores.

"I ran toward the bird market and saw charred pieces of flesh, small spots of blood and several damaged cars," Muhsin said, adding he will no longer visit the Friday market. "I thought that we had achieved real security in Baghdad, but it turned that we were wrong."

The number of Iraqi civilians and security forces killed in January fell to at least 609, an Associated Press tally showed, the lowest monthly death toll since December 2005, and continuing a downward trend since the fall. The figure as tabulated by Iraqi officials in the ministries of Defense, Interior and Health was slightly lower, at 543.

U.S. forces, meanwhile, have expanded offensives in central and northern Iraq, seeking to build on gains against al-Qaida in Iraq in the past year. But the latest campaigns also have driven up the military's death toll after months of decline.

Two U.S. soldiers were killed Thursday _ one by a roadside bomb in Baghdad and another by a rocket or mortar attack on a convoy support center south of the capital, the military reported.

The attacks raised to at least 39 the number of U.S. troops who died in January _ well above the 23 in December but still sharply lower than a year ago. In January last year, 83 soldiers were killed in Iraq.

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Associated Press writers Hamid Ahmed and Sameer N. Yacoub contributed to this report.