When is a civilian not a civilian?

Iraq's leaders say all the people will defend the homeland. So is anybody a fair target?

Ikhlas Faiq was injured on 28 March when a missile fell on the market where she was shopping for her family. When her small son reached up to kiss her in her hospital bed, she sobbed from distress mixed with relief to be alive. Ikhlas is an innocent civilian - no question about that.

But what about 20-year-old Jassem in the next bed? A secondary school student, he is also the kind of young man who might choose or be coerced into joining one of the Iraqi militias currently attacking American and British soldiers. Or he might have in the past - not now, because his arm was amputated after he, too, was hit by shrapnel when the missile hit al-Shula market. Was he an innocent civilian?

The British and American governments said they came to liberate the people of Iraq and bring them humanitarian aid. But now they suspect that Iraqi civilians are really soldiers because the men attacking them are in civilian clothes. "The enemy we're fighting is a bit different from the one we war-gamed against," marvelled Lieutenant General William Wallace, commander of the US army ground forces.

The Iraqi government makes maximum propaganda from civilian casualties such as those in al-Shula market place, even though the deaths may have been caused by rebounding Iraqi anti-aircraft fire. They blame the Americans for "targeting civilians". Then they say that all Iraqis will fight to defend their homeland from the invaders, which turns civilians into combatants.

"Hundreds of thousands of Iraqis are carrying weapons," said the information minister, Mohammed Saeed al-Sahaf. "Rumsfeld says soldiers are putting on civilian clothes. He doesn't understand - an Iraqi may be a schoolmaster or an engineer, but he's still an Iraqi and he'll fight against the invader." In the next breath, Sahaf condemned President Bush as a war criminal for causing civilian deaths. To him, there is no contradiction.

The following day, American troops at a checkpoint near Najaf, fearing a repeat of an incident in which four US soldiers were killed by a suicide bomber at a similar checkpoint, shot at a car that refused to stop. Seven women and children were killed.

According to Human Rights Watch, under international law, the Iraqis could be guilty of "perfidy" - killing the enemy by convincing them that the attackers are non-combatants. "Perfidy poses particular dangers because it blurs the distinction between enemy soldiers, who are a valid target, and civilians and other non-combatants, who are not," it says. "Soldiers fearful of perfidious attacks are more likely to fire upon civilians and surrendering soldiers, however unlawfully."

Are the civilians voluntarily defending their homeland, as the Iraqi government maintains, or have they been forced to fight? In the months leading up to the conflict, the Ba'ath Party distributed thousands of Kalashnikovs to tribal leaders.

"I have a tribe of 200,000 people and 12,000 of them are in Baghdad ready to fight," said a Bedouin sheikh. "There has been growing interest in buying weapons. It's in the interests of Iraqis to have weapons to face the American fighter. We are all military now."

As recently as the past week, party officials were going round Baghdad neighbourhoods offering more weapons, ready for the American assault. Some Iraqis are fighting because they fear being colonised more than they hate Saddam Hussein.

"If someone tries to attack your home, of course you must defend it," said one man.

The militias fall into different types. The most fanatical are the Fedayeen Saddam, under the leadership of Saddam's son Uday. They are true believers, trained to be ruthless and ready for suicide missions if necessary. Then there are the Ba'ath Party militias, organised on a regional basis under the party structures. The tribes operate in their own areas under sheikhs who owe much of their power and wealth to the president. Finally, there is al-Quds army, a popular militia recruited from neighbourhoods in every town and city.

All these groups are armed with Kalashnikovs and rocket-propelled grenades, and their combined force must be more than a million. Their numbers have been swollen by busloads of young men from around the Arab world. The Iraqi government says 6,000 have turned up so far. It regards them as volunteers, like the International Brigades which fought against fascism in Spain; to the Americans, they're terrorists.

According to Taha Yassin Ramadan, the vice-president, the militias are being organised according to a plan whereby each Iraqi who dies takes tens of Americans with him. "We do not want to see any of our men become a martyr for just one or two of them," he said. "Each one will have the objective of killing the largest number of enemy soldiers possible."

The US has the technology and the firepower to prevail in the end, but to do so it may have to kill a lot of civilians. Already the International Committee of the Red Cross has expressed concern about the more than 450 injured and the dozens of women and children killed as US forces battled Iraqis in the small town of Hilla, 60 miles south of the capital.

The Iraqi government may lose, but the diehards could turn themselves into a guerrilla force harassing the occupiers long after victory has been declared.

"The Americans want a short war, but our strategy is based on a long war," said Ramadan.

The western allies may win the war, but their chances of liberating Iraqi civilians from violence and persecution are diminishing daily.

Lindsey Hilsum is the diplomatic correspondent for Channel 4 News