At least nine of the large-scale attacks in Iraq since the beginning of the year have involved the use of chlorine. These bombs strike a particular fear because if people are not killed by the blast, they may easily die an agonising death when the chlorine is dispersed and inhaled.

Chlorine reacts with the water in moist human tissue, such as the eyes, nose, throat and lungs, and forms an acid which then burns the tissue. It was first used as a weapon during the First World War in April 1915 by a German chemist named Fritz Haber who synchronised the release from 6,000 cylinders along a four-mile stretch of the front line. The attack caused the death of about 5,000 allied troops with another 10,000 suffering from inhalation, skin burns and blinding. The following month, Haber returned to his family in Berlin. His wife, Clara, also a scientist, was so repelled by what he had done that she shot and killed herself. Haber won the Nobel Prize in 1918 for his work with ammonia.

The gas bombs have a special significance with Iraqis because of the use of chemical weapons by Saddam Hussein in Halabja 19 years ago. In most cases, the gas is consumed by the explosion, but when a truck bomb exploded in Ramadi in Anbar province on 6 April, scores of people suffered from the effects of chlorine.

It is now established that this tactic has been one of al-Qaeda's gifts to Iraq. Large quantities of chlorine, commonly used in water treatment plants in the Middle East, was stolen in Anbar, where al-Qaeda has a strong presence. A dozen truck bombs loaded with gas cylinders are said by intelligence sources to have been prepared by the group which is seeking, among other things, to dominate Sunni resistance in Iraq and is showing signs of the Khmer Rouge's blood lust.

The pathologies of Iraq are hard to pin down and most people in the West have long given up trying. One bomb follows another; British and American troops are killed at an increasing rate; suicide bombers are able to penetrate the Green Zone in Baghdad and there are signs that the Shia death squads are returning. Even when the bombers struck the capital last week with five separate attacks, the largest of which killed 140 people, the Western media devoted the majority of their attention to the killings at Virginia Tech.

We turn away, taking a perhaps rather odd refuge in the certainty that this is all the fault of the neoconservatives, of the arrogance of Bush and Blair and what is strangely called a policy of 'liberal intervention'. A majority were against the war in 2003 and almost everyone is now.

But this carries you just so far. It is certainly true that none of this would be happening if, in the first place, the invasion had not gone ahead and if, in the second, the Pentagon had not decommissioned the agencies, police force and military units of Saddam's state. But let us just remember a few points before switching channel.

If the number of attacks diminished, the Americans and British troops would leave Iraq far faster than seems likely at the present. The situation, therefore, can no longer be taken for a classic resistance of an occupying force. Nor can it be entirely seen as the opposite, that is to say a guerrilla war that is maintained by Islamist, Shia and Ba'athists groups for the sole purpose of engaging the American and British military.

The proof of this lies in the fact that the great majority of casualties are caused by Arabs killing Arabs, Muslims slaughtering Muslims.

This brings us back to the chlorine bombs being built by al-Qaeda to terrorise and kill their Muslim brothers, who, we must remember, were so recently oppressed by the atheistic regime of Saddam Hussein. It is as if Protestant and Catholic groups in the French Resistance used the Nazi occupation to blow up each other's churches and market places and slaughter each other's children. Actually, it is weirder in Iraq because the Sunni extremists of al-Qaeda are killing and torturing more Sunnis than Shia, let alone US soldiers.

The thought process is psychopathic: it has the same logic we heard in the ravings of the gunman at Virginia Tech. There is a similarity of exhibitionism, too, a need for attention that must escalate the horror to maintain some kind of foothold in the Western news bulletins. These monsters in Iraq must have felt a mite frustrated by the events on an American campus last week, especially as a double attack on a university campus in Baghdad in January killed twice as many students but rated a mere day's coverage in the West.

So we are talking about civil war and the convergence in Iraq of a number of opportunistic death cults, the most crazed and narcissistic of which is probably al-Qaeda, though the Shia death/torture squads fielded by Muqtada al-Sadr run a pretty close second. Is this Bush and Blair's fault? Ultimately, yes because they opened the fissure that released the superheated gases of Islamist fanaticism.

But we cannot leave it at that. Somewhere in Iraq, for example, there is an individual who allowed two young children to travel into Baghdad as passengers in the back seat of car that was loaded with explosives. Naturally enough, the children's presence lowered suspicion at the checkpoints. The car entered the city, the adults hopped out and detonated the bomb with the children still inside.

That is badness of a high order and you would expect it to have offended every loving parent across Islam. You would certainly expect to hear some stern religious voices in Middle East calling for the cessation of such barbarity in the name of one or other sect or tribe or, indeed, Allah. There are murmurs of disquiet, even horror, but in a way, the Americans and British have become everyone's alibi or at least plea of mitigation.

Our catastrophic blunder has removed the need for any moral calibration in Islam of what Muslims are doing to Muslims in Iraq. In the West, there are many, who, because they were passionately against the war, fail to see that they ought to refine their judgment on the men who thrill to the idea of perfecting a chlorine bomb that will maim, blow apart or asphyxiate the workman who has just got off shift, the housewife loaded down with groceries, the student waiting to meet a friend. The chlorine bombers are not freedom fighters

There is nowhere for us to go on Iraq. There is darkness but no hint of dawn. The surge of troops that has put such a strain on the US military has reached the halfway mark with about 15,000 deployed. In the same period, the civilian death toll has risen by 15 per cent. More troops mean more deaths, but fewer troops may mean even more deaths: a sprawling civil war that could last five to 10 years and change the course of world history on a very grand scale indeed.

There may be just a few opportunities to save the region. The first comes in early May when the US Secretary of State, Condoleezza Rice, meets the Foreign Ministers of Iraq's neighbours in Egypt. The era of what has been called Bush's 'moralising foreign policy' is over and Dr Rice is said to be on a mission to listen.

It is hoped that bilateral talks with Syria and Iran will take place afterwards, but America and Britain need to show much more penitence for the ungodly mess we have created. Among the Middle Eastern powers, there has to be recognition that many of the demons let loose in Iraq are the product of religious fanaticism.

The Muslim world has to find its own way of speaking up for humanity and civilisation and, for a start, to condemn the chlorine bombs.

henry.porter@observer.co.uk