In Iraq, a country being torn apart in a seemingly never-ending conflict, there is now an acute shortage of blood. And the worse the violence becomes, the higher its black market prices rise.

Faced with the crisis, the medical authorities will supply blood for operations and treatment only if families or friends of the victims can provide an equal amount in return. There are exceptions for the most serious of cases, when up to two litres are given free.

But on many occasions, relatives are unable to donate the blood because they are too old or ill themselves, or because they have a blood type the hospitals do not want because they already a preponderance of it.

And into this gap in the market fit people like Ali Mahmood Hashim, who, unemployed with three children to feed, is selling the only thing of worth he has left. "There is nothing else I can do," he said outside the Bab al-Modam medical complex in central Baghdad. "Everything is expensive and we have no money. I am not forcing anyone to buy my blood, but there are always those willing to pay for it."

The prices of blood vary from 20,000 to 40,000 dinars per litre, with the negative type fetching more because of its comparative rarity. The sellers will either give blood, pretending to be a relative of the victim, or provide it already extracted, in a bottle.

It is unclear whether selling one's own blood is legal. The sellers are routinely arrested by police but recently a judge ruled that it is not strictly against the law. However, there do exist rules about how often someone can give blood - regulations of which the sellers are in clear breach.

The National Blood Transfer Centre at Bab al-Modam, the largest in Iraq and the only one in Baghdad, is situated alongside three medical colleges and a large cemetery. It is also around the corner from Haifa Street, a notoriously dangerous thoroughfare where bombings and ambushes against US and Iraqi military patrols take place almost every day. The Americans are evacuated to the Green Zone, but some of the Iraqis on both sides end up at Bab al-Modam. Alwan Jaseem Mohammed, 33, is the car-park supervisor at the medical complex. He saw the lucrative blood trade going on around him and decided to join in. "I am not doing anything to feel shame. I am saving people's lives," he said. "I have now done it four times and each time the relations have given me a 'gift'. The ones who are poor gave me 10,000 dinars, but I have received up to 40,000 dinars. I have never obliged anyone to pay me."

Kardam Khalid Ismail runs a kiosk near by selling soft drinks, sweets and cigarettes. He is 27 years old and looks pale with a distinctive yellow tinge to the whites of his eyes. "Yes, I sell blood. But I do not think it is a crime at all," he said. "Sometimes I go in disguise, with longer or grey hair, or with a false beard, to make sure the people at the blood centre do not recognise me."

As well as the police, the men keep an wary eye out for "bosses", local hardmen who run syndicates of blood-sellers. Ahmad Nazaar Hassan, known as "the crocodile", heads such a group. He came immediately to the point: "You will get very good blood for 40,000 dinars... Ah, you are a journalist, then it'll be 50,000," he chortled.

One buyer, Gaith Saleh Salman, a 45-year-old teacher, ran out of the clinic. "Who will give me negative blood?" he shouted. "I will pay whatever it takes. My wife is at al-Rahibad hospital. It is a private hospital but even there they have not got the negative type. I am desperate." But there was no one with negative blood willing to sell and he walked back dejectedly.