Baghdad: When police came hunting for a 19-year-old woman they believed had been recruited by Al Qaida to be a suicide bomber in a town north of Baghdad, they found she was already dead: Slain by her father, who told police he strangled his daughter out of shame and then cut her throat.

The killing of Shahlaa Al Anbaky, reported by police Friday, appeared to be from an unusual melding of motives - part to defend the family honour, part to prevent her from joining the militants. But how much of each weighed in her father's mind remains unclear, with police still investigating the details.

Al Qaida has been recruiting women for suicide attacks because they can pass police checkpoints more easily than men by concealing explosives under an abaya, a loose, black cloak that conservative Muslim women wear. Suicide bombers have been Al Qaida's most lethal weapon in Iraq, killing hundreds of civilians and members of Iraq's security forces.

The slaying took place in the town of Mandali, about 100 kilometres northeast of Baghdad in Diyala province, which only a few years ago was one of Iraq's deadliest regions, torn by attacks by Al Qaida and Sunni insurgents and vicious sectarian killings between Sunnis and Shiites.

After Sunni tribal militias turned on Al Qaida, the province has become much safer, like much of Iraq. But Al Qaida militants still carry out deadly attacks in the area.

Authorities were still trying to put together a complete picture of the killing.

A Diyala police spokesman, Maj. Ghalib Al Karkhi, said security forces had information the young woman had ties to Al Qaida and raided her father's home Thursday. When questioned by police, the father, Najim Al Anbaky, told police he killed his daughter a month earlier because he found out she intended to blow herself up in a suicide attack for Al Qaida.

The father, described by authorities as a small-time trader of chickens and sheep, led police to her grave in the backyard. The woman had been strangled and then her throat cut for good measure, Al Karkhi said.

A senior Iraqi army official involved in the case gave a slightly different account, saying authorities looking for the daughter called the father in for questioning, not knowing Shahlaa was dead. It was then the father confessed to killing her, said the official, who spoke on condition of anonymity because he was not authorised to talk to the press. The different accounts could not immediately be explained.

Authorities dug up her body in hopes of learning more about how the killing happened. But the true reason behind the crime will likely remain a mystery.

The father was still in custody under investigation, though no charges had been filed so far, and other family members could not be reached for comment.

Another police official, also speaking on condition of anonymity to discuss the case, said authorities were investigating the possibility that the woman had a boyfriend in Al Qaida.

Police records indicated that Najim Al Anbaky killed one of his sisters in 1984 in what was described as an honour killing, the official said.

A range of motives may have played a part in the killing - a strong hatred of Al Qaida in a part of the country where the group once terrorised residents, fear that the family would be punished if she carried out a bombing, anger or shame that she might be romantically involved.

So-called "honour killings" do take place in Iraq's traditional, tribal society - though their extent is little measured, overshadowed by the political violence that has bloodied the country since the 2003 US- led invasion. In such cases, a man is said to be trying to reclaim the family honour by killing a sister, daughter or mother if there's a suspicion she has had improper relations with men outside the family. Courts and authorities sometimes turn a blind eye to such slayings.

While they are not as common as male suicide bombers, women suicide bombers can be just as deadly.

Terrorists have long recruited Iraqi women to carry out such attacks. As security has tightened across the country, women can get past security checkpoints because there are rarely enough women police officers to inspect every woman passing by.

A female suicide bomber was behind one of the deadliest attacks this year in Iraq, after she blew herself up among Shiite pilgrims in Baghdad in February, killing 54 people. In April of last year, more than 60 people died when two female suicide bombers hiding explosives in their purses struck worshippers streaming into Baghdad's most important Shiite shrine for Friday prayers.