The two bombers struck at Baghdad's police academy on Tuesday, killing at least 36 officers and cadets and wounding more than 50, officials said.
Confusion surrounded the gender of the two bombers. Bayan Baker Solagh, the Iraqi Interior Minister, said the attacks were carried out by two Iraqi policewomen.
However, al-Qaida in Iraq, claiming responsibility for what is the bloodiest attack in three weeks, said in an internet statement that "two brothers" had carried out the attack on a police force it said was persecuting Sunni Arabs.
The Shia-led government, facing an election next week amid daily violence, denies such accusations.
The US military initially blamed the attack on two female bombers, later saying they were male.
Also on Tuesday, Iraqi police said they had discovered nine bodies with gunshot wounds near a mixed Shia and Sunni Arab town south of Baghdad.
The bodies of the men in their 30s, apparently civilians, were discovered near Musayyib, south of Baghdad. They had all been shot at close range, said police.
Elsewhere around the country, 11 other Iraqis, mainly from the security services, died in other violence.
Many security services members
died in violence across the country
The flurry of deadly attacks targeting security officials have heightened concerns about increased unrest in the run-up to Iraq's election on 15 December for the first post-invasion parliament on a four-year term.
In Saddam Hussein's hometown of Tikrit, north of the capital, two council workers were killed and a third abducted.
In Salah al-Din, three members of the northern Iraqi oil company's security force were killed as they patrolled a pipeline near Sherqat.
In the village of al-Khalis, north of Baquba, one of Prime Minister Ibrahim al-Jaafari's bodyguards was killed in a drive-by shooting.
Al-Jaafari was on an official visit to Tokyo, and the bodyguard had been on his way to visit his family.
On the road between Baghdad and Baquba, an Iraqi army colonel and his driver were found shot dead, police said.
Baquba has seen many attacks
on US and Iraqi forces
Baquba - the site of an ongoing revolt - was on Saturday rocked by an attack on an Iraqi army convoy that killed 19 soldiers.
In Baghdad, the Interior Ministry said police General Hamza Hussein Fadel and a passenger in his car had been shot dead by unknown attackers in the capital's southern Dura district.
A policewoman was shot dead in Baghdad's western Amriyah district.
Meanwhile, in Karbala, a Salafist (follower of a strict interpretation of Sunni Islam) was sentenced to death for his alleged involvement in a December 2004 attack in the Shia city, a judicial source said.
Faiz Jalil Shaalan was sentenced to death by a criminal court. He was arrested following a bomb attack in which Shaikh Abd al-Mahdi al-Karbalai, a representative of Shia Grand Ayat Allah Ali al-Sistani, was wounded.
Seven people were killed and another 30 wounded in the sectarian attack, which happened near the tomb of Imam al-Hussein, the Prophet Muhammad's grandson, whom the Shia revere.
The death penalty, originally suspended by the Americans following the invasion of Iraq in March 2003, was reinstated by the US-backed interim Iraqi government in June 2004.