Leading article: Iraq is being ethnically cleansed, and our troops can do nothing

The worst and most frightening things take place in secret. There is a sinister logic to this, because when violence reaches a certain level of sadistic intensity and terrifying unpredictability, television cameras tend not to be present.

So it was in Bosnia in the spring and summer of 1992, where hundreds of small grisly massacres unfolded separately but more or less at the same time, far from the apparently all-seeing eye of CNN in Sarajevo, in villages strung out all over the north and east of Bosnia.

So it is now in Iraq, where, as The Independent's Patrick Cockburn reveals today, whole populations are on the move as a silent but deadly campaign of ethnic cleansing rids once ethnically and confessionally mixed provinces of now unwanted minorities. This destructive process appears to be proceeding far from the world's gaze in the province of Diyala, north of Baghdad, close to the Iranian border, where Sunni militants are driving out local Kurdish and Shia families who have lived in peace with their neighbours for generations.

The exodus of middle-class Iraqis from Baghdad and the other big cities to Jordan, Syria, Egypt and - if they are lucky - the West, is a better-documented phenomenon. The numbers are pretty huge; one million Iraqis are now living in Jordan, while Iraq has issued over 1.85 million passports in the last 10 months - most, it is presumed, to emigrants.

Their plight is to be pitied, as is that of Iraq, for their flight robs the country of its educated elite - of those who it was once hoped might lead Iraq's reconstruction. But at least the younger among them have a chance of making a new life.

Not so these rural refugees from sectarian fury. No one even has the slightest idea of how many victims there are of these outrages, as so few outsiders dare to venture into their areas.

These rural refugees also have next to no chance of reaching any real sanctuary. Without the money, the schooling, the relevant documents or the connections to get them a berth in exile, their only destiny would appear to be a twilight existence spent in makeshift hovels among fellow Kurds, Shias or Sunnis in communities too poor to lend them much material aid or even sympathy.

So, what is to be done? The problem with ethnic cleansing, as the sad experience of the Balkans in the 1990s showed clearly, is that it is usually irreversible. Once it starts, it has a momentum of its own, and is correspondingly difficult to stop. When part of a minority group leaves a village, the rest soon feel too frightened to stay. They don't want to find out the hard way if it is safe to remain.

The presence of British and American troops does not appear to be making a blind bit of difference, either. Hunkered down in their bases, in largely hostile urban settings, the occupation forces have neither the will nor the means to patrol each and every remote village in such a large country in order to ensure that Shias, Kurds and Sunnis treat each other civilly.

The depressing conclusion one must draw from the disturbing news coming out of the provinces of rural Iraq is that whether we stay or go is no longer especially relevant to the unfolding civil war.

The claim routinely made by George Bush and Tony Blair that our presence is required in Iraq if only to prevent the outbreak of a civil war, therefore, is no longer plausible.

As a civil war is already taking place, they must come up with a new rationale for keeping troops in Iraq, or, unlikely though that sounds, produce a new plan for tackling the sectarian conflict that their invasion has undoubtedly helped to ignite.