As al-Tallal, 50, walked towards her house, one of three men in the Opel stepped out and raked her with bullets.

A women's rights campaigner, Umm Salam - a nickname - knows about the three men in the Opel: they tried to kill her on 11 December last year. It was a Sunday, she recalls, and 15 bullets were fired into her own car as she drove home from teaching at an internet cafe. A man in civilian clothes got out of the car and opened fire. Three bullets hit her, one lodging close to her spinal cord. Her 20-year-old son was hit in the chest. Umm Salam saw the gun - a police-issue Glock. She is convinced her would-be assassin works for the state.

The shootings of al-Tallal and Umm Salam are not isolated incidents, even in Najaf - a city almost exclusively Shia and largely insulated from the sectarian violence of the North. Bodies of young women have appeared in its dusty lanes and avenues, places patrolled by packs of dogs where the boundaries bleed into the desert. It is a favourite place for dumping murder victims.

Iraqis do not like to talk about it much, but there is an understanding of what is going on these days. If a young woman is abducted and murdered without a ransom demand, she has been kidnapped to be raped. Even those raped and released are not necessarily safe: the response of some families to finding that a woman has been raped has been to kill her.

Iraq's women are living with a fear that is increasing in line with the numbers dying violently every month. They die for being a member of the wrong sect and for helping their fellow women. They die for doing jobs that the militants have decreed that they cannot do: for working in hospitals and ministries and universities. They are murdered, too, because they are the softest targets for Iraq's criminal gangs.

Iraq's women live in terror of speaking their opinions; of going out to work; or defying the strict new prohibitions on dress and behaviour applied across Iraq by Islamist militants, both Sunni and Shia. They live in fear of their husbands, too, as women's rights have been undermined by the country's postwar constitution that has taken power from the family courts and given it to clerics.

'Women are being targeted more and more,' said Umm Salam last week. Her husband was a university professor who was executed in 1991 under Saddam Hussein after the Shia uprising. She survived by running her family farm. When the Americans arrived she got involved in civic action, teaching illiterate women how to read and vote, independent from the influence of their husbands. She helped them fill in forms for benefits and set up a sewing workshop.

In doing so she put herself at mortal risk. And since the assassination attempt, like many women in Najaf, she has found it hard to work. Which is what the men in the white Opel wanted. To silence the women like Umm Salam, who is 42.

'It is very difficult for women here. There is a lot of pressure on our personal freedoms. None of us feels that we can have an opinion on anything any more. If she does, she risks being killed.'

It is a story familiar to women across Iraq, betrayed by the country's new constitution that guaranteed them a 25 per cent share of membership of the Council of Representatives. That guarantee has turned instead into a fig leaf hiding what women activists now call a 'human rights catastrophe for Iraqi women'.

After a month-long investigation, The Observer has established that in almost every major area of human rights, women are being seriously discriminated against, in some cases seeing their conditions return to those of females in the Middle Ages. In areas such as the Shia militia stronghold of Sadr City in east Baghdad, women have been beaten for not wearing socks. Even the headscarf and juba - the ankle-length, flared coat that buttons to the collar - are not enough for the zealots. Some women have been threatened with death unless they wear the full abbaya, the black, all-encompassing veil.

Similar reports are emerging from Mosul, where it is Sunni extremists who are laying down the law, and Kirkuk. Women from Karbala, Hilla, Basra and Nassariyah have all told The Observer similar stories. Of the insidious spread of militia and religious party control - and how members of those same groups are, paradoxically, increasingly responsible for the rape and murder of women outside their sects and communities.

'There is a member of my organisation, an activist who is a Christian,' said Yanar Mohammed, head of the Organisation for Iraqi Women's Freedom, who has had death threats for her work in protecting women threatened by domestic violence or 'honour' killings. 'She would have to walk home each day to her neighbourhood through an area controlled by one of the Islamic Shia militias, the Jaish al-Mahdi. She does not wear a veil so she gets abused by these men. About three weeks ago, one of them starts following her home saying that he wants a sexual relationship with her. He tells her what he wants to do, and if she doesn't agree he says she will be kidnapped. In the end he thinks that, because he is armed, because he threatens her existence, she will have to agree to a "pleasure marriage" [a temporary sexual union arranged by a cleric].'

Strong anecdotal evidence gathered by organisations such as that of Yanar Mohammed and by the Iraqi Women's Network, run by Hanna Edwar, suggests rape is also being used as a weapon in the sectarian war to humiliate families from rival communities. 'So far what we have been seeing is what you might call "collateral rape",' says Besmia Khatib of the Iraqi Women's Network. 'Rape is being used in the settling of scores in the sectarian war.' Yanar Mohammed describes how a Shia girl was kidnapped, raped and dumped in the Husseiniya area of Baghdad. The retaliation, she says, was the kidnapping and rape of several Sunni girls in the Rashadiya area. Tit for tat.

Similar stories are emerging across Iraq. 'Of course rape is going on,' says Aida Ussayaran, former deputy Human Rights Minister and now one of the women on the Council of Representatives. 'We blame the militias. But when we talk about the militias, many are members of the police. Any family now that has a good-looking young woman in it does not want to send her out to school or university, and does not send her out without a veil. This is the worst time ever in Iraqi women's lives. In the name of religion and sectarian conflict they are being kidnapped and killed and raped. And no one is mentioning it.'

Women activists are convinced there is substantial under-reporting of crimes against women in some areas, particularly involving 'honour killing' - there is a massive increase against a background of pervasive violence - and that families often seek death certificates that will hide the cause. In regions such as the violent Anbar province, the country's largest, which borders Jordan and Syria, there is little reporting of the causes of any death. And activists complain, in any case, that they have been blocked from examining bodies at the Medical Forensic Institute in Baghdad, or collecting their own figures to build up an accurate picture of what is happening to women.

While attacks on women have long been the dirty secret of Iraq's war, the sheer levels of the violence is now pushing it into the open. Last week in Samawah, 246 kilometres (153 miles) south of Baghdad, three women and a toddler were killed when gunmen stormed their home in an unexplained mass murder. Like Dr al-Tallal in Najaf, they were Shia Muslims in a Shia city. The three women were shot. The 18-month-old baby had her throat slit.

In the north, too, last week the killing of women became more visible, with the al-Jazeera network reporting that attacks on women in the city of Mosul had led to an unprecedented rise in the number of women's bodies being found. Among them was Zuheira, a young housewife, found shot dead in the suburb of Gogaly. Salim Zaho, a neighbour, quoted by the television station, said: 'They couldn't kill her husband, a police officer, so they came for his wife instead.'

It is one of the recurring narratives of murder told by Iraqi women. It is a violence that would not be possible without a wider, permissive brutalising of women's lives: one that permeates the 'new Iraq' in its entirety. For it is not only the religious militias that have turned women's lives into a living hell - it is, in some measure, the government itself, which has allowed ministries run by religious parties to segregate staff by gender. Some public offices, including ministries, insist on women staff wearing a headscarf at all times. A women's shelter, set up by Yanar Mohammed's group, was closed down by the government.

Most serious of all are the death threats women receive for simply working, even in government offices. Zainub - not her real name - works for a ministry in Baghdad. One morning, she said, she arrived at work to find that a letter had been sent to all the women. 'When I opened up the note it said, "You will die. You will die".'

The situation has been exacerbated by the undermining of Iraq's old Family Code, established in 1958, which guaranteed women a large measure of equality in key areas such as divorce and inheritance. The new constitution has allowed the Family Code to be superseded by the power of the clerics and new religious courts, with the result that it is largely discriminatory against women. The clerics have permitted the creeping re-emergence of men contracting multiple marriages, formerly discouraged by the old code. It is these clerics, too, who have permitted a sharp escalation in the 'pleasure marriages'. And it is the same clerics overseeing the rapid transformation of a once secular society - in which women held high office and worked as professors, doctors, engineers and economists - into one where women have been forced back under the veil and into the home. The result is mapped out every day on Iraq's streets and in its country lanes in individual acts of intimidation and physical brutality that build into an awful whole.

And so in Salman Pak, on the Tigris 15 miles south of Baghdad, The Observer is told, the Karaa Brigade of the Ministry of the Interior rounds up some Sunni men. Later some of the police return to the men's houses and promise their worried women to help find the missing men in exchange for sex.

In the Shia neighbourhood of al-Shaab in Baghdad, militiamen with the Jaish al-Mahdi put out an order banning women from wearing sandals and certain shoes, skirts and trousers. They beat up others for wearing the wrong clothes.

In Amaryah, a Sunni stronghold in Baghdad, Sunni militants shave three women's heads for wearing the wrong clothes and lash young men for wearing shorts. In Zafaraniyah, a largely Shia suburb south of Baghdad, the Jaish al-Mahdi militiamen wait outside a school and slap girls not wearing the hijab.

It is a situation bleakly recorded by the Human Rights Office of the UN Assistance Mission to Iraq. 'There are reports that, in some Baghdad neighbourhoods, women are now prevented from going to the markets alone,' Unami reported. 'In other cases, women have been warned not to drive cars, or have faced harassment if they wear trousers. Women have also reported that wearing a headscarf is becoming not a matter of religious choice but one of survival in many parts of Iraq, a fact particularly resented by non-Muslim women. Female university students are also facing constant pressure in university campuses.'

'Since the beginning of August it has just been getting worse,' says Nagham Kathim Hamoody, an activist with the Iraqi Women's Network in Najaf . 'There are more women being killed and more bodies being found in the cemetery. I don't know why they are being killed, but I know the militias are behind the killing... We went to the mortuary here in Najaf, but the authorities would not co-operate in helping to identify the murdered women. There was one doctor, though, who told us that some of the bodies showed signs that they had been beaten prior to their murder.'

And so the painful lives of Iraqi women go on.