The concrete blast barrier topped with razor wire has become the symbol of America's occupation of Iraq. Thousands of tonnes of concrete have transformed buildings frequented by foreigners into fortresses, while barriers block the roads past military installations and hotels, snarling up the traffic for hours. At the Palestine Hotel, home to journalists and the American contractor Kellogg, Brown and Root, Thursday is the traditional evening for middle-class Iraqis to hold wedding banquets. Brides in white satin, surrounded by drummers and dancers, are frisked by newly trained Iraqi guards before trooping along a narrow, dusty alleyway between 15ft-high blocks that would not have looked out of place in Colditz.
After the synchronised attacks on the International Committee of the Red Cross and four police stations, heavy trucks brought hundreds more tonnes of concrete to police stations around the capital. In Adhimiya, an area renowned for still harbouring loyalists to Saddam Hussein, uneasy police officers in new blue uniforms watched in silence as a crane carefully lowered its massive load in front of their new office. American troops supervised the uncoiling of yet more razor wire. I asked a soldier whether he thought concrete was the answer, but he could not hear my question. His eardrum had been perforated by the blast. Asked about the dangers to policemen, the presiding Iraqi police officer gave what passes for a neutral answer here: "We are Muslims and we believe in God, so we don't worry about whether it's more risky to be a policeman or a civilian. It's all the same to us. Those who fear death are too attached to this life."
Policemen and security guards are on the front line in this war. The police, once reviled as corrupt stooges for Saddam, are now targeted as collaborators. But there is no shortage of recruits - there is 60 per cent unemployment in Iraq and policemen earn $120 a month, a decent salary. The concrete barriers prevent suicide car bombers from reaching their targets, but instead the driver smashes against the barricade. Those inside the building have a good chance of survival, but security guards outside and passers-by are more likely to die. At the Red Cross, two guards were killed along with ten people in a truck that happened to be driving past at the fatal moment.
It is easy to point out that the freedom which President Bush claims to have brought to Iraq is turning the capital into a city of prisons. Anyone who can shelters behind concrete. But, as yet, no one has thought of an alternative. Even if they had enough soldiers to mount more patrols and checkpoints, that would just create more resentment. The country is already too militarised for most Iraqis, who may not wish the Americans to pull out instantly, but still feel humiliated by the visible signs that they are being ruled by foreigners in their own land. According to Bush, last Monday's attacks showed the "desperation" of those who would violently oppose the US occupation of Iraq, their response to the progress America has brought. That is not how it looks from Baghdad, where many are shocked that so many bombs could be co-ordinated, a sign that the network of resistance is growing more sophisticated and better organised. There is no evidence that they are on the run, nor that the Americans really know who "they" are.
Last Monday, Brigadier General Mark Hertling in Baghdad declared that the attacks "have a mode of operation of foreign fighters", while the same day, further north, Major General Raymond Odierno said confidently that the resistance contained only a "very, very small percentage of foreign fighters". The British know, from Malaya to Northern Ireland, that intelligence is the key to fighting a guerrilla war, and the American confusion about the nature of the enemy shows how difficult that is proving in Iraq. Someone must have seen the men who turned a trailer for carrying a generator into the rocket launcher that fired at the Al Rashid Hotel while the US deputy secretary of defence, Paul Wolfowitz, was staying there. But no one breathed a word. In Beyji, a sullen town north of Tikrit, where the oil pipeline is frequently blown up and American patrols are constant targets for grenade and rocket attacks, US soldiers rely on children for information.
"They like to tell us if they've seen their daddies or their uncles shooting weapons," said Sergeant John Letts of the 3rd Battalion, 66th Armoured Regiment. More savvy than most, he glad-hands shopkeepers in the souk and tries to keep his ear to the ground. He has no illusions. "It seems a lot of them do want to be your friend, but I have a feeling that a lot of times there's a hidden agenda underneath - they're trying to get information from us while we're trying to get information from them. It's a two-way street." His unit has had just one day's training in guerrilla warfare.
Humanitarian aid workers face an acute dilemma. After the bomb at the UN's Baghdad headquarters in August, nearly all aid agencies reduced their foreign staff and their profile, and some may retreat even further after the Red Cross attack. Education and skills levels are reasonably high in Iraq, so Iraqis are quite capable of doing the work. However, sanctions cut them off from the world for 13 years, and many organisations would like also to employ foreigners with experience of other crises. "We've got sandbags, barbed wire, towers - this is not the way to do humanitarian aid," said Larry Hollingworth, UN humanitarian co-ordinator in Baghdad and a veteran of Bosnia, Rwanda and almost every other catastrophe of the past two decades. "We just had the Madrid donors conference - they said, bring in $31bn and we'll spend it. But how can we spend it if we can't get out? We've tried high profile, we've tried low profile, and we're all now re-evaluating just what we can do. If we leave, do the terrorists win? I think we have reached a great crossroads in humanitarianism. We've come to the situation where maybe the only way ahead is that we have protection."
Some aid agencies are looking to private security companies, which are already protecting US and European companies. Bechtel, the biggest corporation here, expects to spend $40m on security in the first 18 months of its billion-dollar contract in Iraq. It employs 100 guards from ArmorGroup to protect 164 foreign employees. Hollingworth suggests that another approach could be to get a country that is not part of the occupying coalition to send soldiers with a specific mandate to protect humanitarian workers. However, a guerrilla force that does not distinguish between a US soldier and a Red Cross worker is not going to respect the neutrality of Sweden or Switzerland.
The Green Zone, which houses Iraq's government, the Coalition Provisional Authority, is a vast closed compound where US companies recreate as best they can the American way of life. The effect is to cut them off from Iraq, but it is hard to see what else they can do at this stage. "The humanitarians tried to find space away from the CPA," said Hollingworth. "Yet we're now being forced closer and closer to it, because how else can we survive?"
For Iraqis, the choices are even more stark. For the foreseeable future, all government jobs and many in private companies doing reconstruction work depend on the provisional authority. There is little alternative employment and no social security safety net. The guerrillas have made it clear that they do not care how many Iraqis they kill, and concrete blast blocks will not deter them.
Lindsey Hilsum is diplomatic correspondent for Channel 4 News