Leading article: The ominous nature of this horrific violence

The tide of violence in Iraq continues to rise. Yesterday, more than a hundred Iraqis died after a suicide car-bomb exploded in the north of Baghdad. It was the deadliest attack in the country since February. Yet this was only one of a series of attacks that took place across Baghdad during the day. Nor is the situation any better in the provinces. Dead bodies are turning up in the villages surrounding the capital. Seventeen men were executed north of Baghdad yesterday by unidentified gunmen who were wearing military uniforms. And last week two British soldiers were killed in a roadside bombing in southern Iraq.

It is increasingly clear that what lies behind much of the violence is sectarianism. Tit-for-tat killings between Shia and Sunni militants are escalating. The suicide attacks orchestrated by the al-Qa'ida leader, Abu Musab al-Zarqawi, are clearly designed to exacerbate sectarian tensions. And it appears that, after many months of restraint, the Shia of Iraq are beginning to respond in kind. The spread of the violence to Basra in the Shia-dominated south is a distinctly ominous sign.

The sectarian division in Iraq goes deeper than is often appreciated. When a military engagement takes place it is usually depicted as a battle between "insurgents" and "Iraqi government forces". But this is only part of the story. In the recent capture of Talafar in the north, for instance, Kurds and Shia Turkmen - backed by US troops - routed Sunni Turkmen and Sunni Arab fighters. The battles for Iraq's future are increasingly breaking down along sectarian lines.

The fear of full-blown civil war is spoken of openly in Iraq these days. Indeed, a considerable number of Iraqis believe that the US wants to provoke such a religious and sectarian crisis in order to divide the country. This is a classic Middle East conspiracy theory, of course. It is firmly in the US interest for Iraq to remain united. Yet the fact that such a theory is gaining ground is a disturbing indication of where Iraq might be headed.

Meanwhile, the US military in Iraq continues to apply its influence to often dangerous effect. Yet another grand US operation is taking place in northern Iraq, this time to choke off the supply of foreign fighters supposedly coming into Iraq from Syria. Yet the idea that the backbone of the insurgency is foreign is distinctly questionable. Some suspect this operation is more geared towards backing up US propaganda than tackling the roots of the insurgency. But that is not to say that such operations do not have a fearful cost. As in Fallujah, innocent civilians are inevitably going to be caught in the cross-fire. The result will be the further alienation of the Iraqi population from the US military presence.

This horrifying level of bloodshed overshadows everything else that occurs in Iraq. Yesterday, some last-minute revisions were made to the Iraqi constitution: the Arab League's charter will now be recognised; Iraq's water resources will be managed by central government rather than provincial authorities. The final draft of the constitution will now be presented to the United Nations. In a month's time, Iraqis will vote on whether to accept it or not. But how many more Iraqis will have died in that time? And how badly will inter-religious relations have been damaged?

Iraqi civil war is not yet inevitable. Inter-marriage between Sunnis and Shias is relatively common in some parts of Iraq. There are still large mixed areas. And, importantly, a substantial number of people still claim to feel Iraqi, and are less willing to be defined by their ethnicity or faith. But, with each new day of violence, the strength of the moderates is diminished - and, with each fresh atrocity, the chasm of civil war opens a little wider.