In the spring of 2003 Dahr Jamail, a fourth-generation Lebanese-American with a taste for adventure, was up a mountain in Alaska, climbing and earning a living by working as a guide. He was, though, following news of the invasion of Iraq, and what he read and heard made him so furious that he decided to leave the mountains - "my church", as he calls them - and head for that newly subjugated land, armed only with a laptop and a digital recorder.

In a world of gung-ho, embedded, flak-jacketed US reporters telling the tale from the military angle, he had decided to try to find out what was happening to the Iraqis, who seemed absent from the story, which was odd considering there were 29 million of them in the country, dodging the bombs and the bullets. Or not.

"I wanted to report on where the silence was," he says. "There's this huge story going on and nobody's talking about it. How are Iraqis getting by, what's their daily life like?"

Jamail, a spruce 39-year-old who is the author of a new book, Beyond the Green Zone, says the supine nature of the US media encouraged him to act. "With a few exceptions, most of the US mainstream was just stenography for the state," he says. "It wasn't journalism; it was writing down what the Bush administration was telling them. I was amazed and outraged. I felt that the lack of clear information was the biggest problem I could see in the US, so I decided I should go over and write about it."

It took him until November 2003 to get the money together - $2,000, everything he had - and make some contacts, via the internet, in Iraq. He flew to Amman in Jordan, found a driver and an interpreter - he spoke no Arabic - and took a car to Baghdad, accompanied by a young couple from the UK who intended to spend a few days there "for the experience". The border was unguarded, US troops notable by their absence. The war had been fought at long range; now there was a vacuum.

Jamail visited hospitals and went to the town of Samarra, 50km north of Baghdad, to check out a "firefight" in which the US military said they had been attacked and had killed 54 Iraqi fighters. Jamail found the locals telling a different story: two Iraqi fighters had attacked a detachment of US troops guarding a delivery to a bank, and the soldiers had responded by firing indiscriminately, killing and wounding many civilians.

At first he had no intention of trying to compete with the mainstream media. "For the first two weeks [of a nine-week stay] I was just sending emails back home," he says. "I had a list of a little over a hundred friends, mostly in Alaska. I would go out in the day with an interpreter - I found someone to work with me who was really cheap because I didn't have much money - and interview people, take amateur photos, and then go back to the hotel and write it up. It was essentially blogging, but I didn't know what blogging was and I didn't have a blog, of course. I was just sending out two, three, four, five pages a night with a few photos attached to friends.

"After about two weeks someone suggested, 'Hey, you should post on this website electroniciraq.ne.' They wanted posts from people on the ground. I did that for about a month and then towards the end of my trip, with about two weeks to go, I was contacted by the BBC to do a little bit of work with them. A start-up website in New York also contacted me to start doing some stories. I actually got paid to do some work, and that's when it became clear I could actually come back and work as a journalist."

I try to probe why Jamail should have made this extraordinary gesture: was there something in his make-up that led him to take this stand? Born and raised in Texas, the son of a grocery store owner, he says that there is a streak of unpredictability in his family. He is the youngest of three: his sister is a pilot, his brother is a police officer. "My parents have always had their hands full and were broken in a bit, so I guess they weren't completely shocked when I started to do my thing," he says. He means climbing, but what about Iraq? How did they and others close to him react? "Most people thought I was crazy. My closer friends supported it. They felt, 'If this is what you think, and you really want to do it, then all power to you.' I decided, wrong or right, not to worry my parents about it until I got in there, so I waited and wrote [to] them after I reached Baghdad. Fortunately they were open to it; they were shocked, but they were open to it."

Before he headed for Alaska in 1996, Jamail had worked as a chemical technician on Johnston Island, an atoll in the Pacific where the US military had dumped parts of its obsolete stockpile of chemical weapons - no problem here finding weapons of mass destruction. Jamail was there to check air quality in a pilot plant designed for decommissioning the weapons, but became disillusioned when he thought results were being rigged and leaks covered up.

It is tempting to see that disillusionment as the key to his later engagement, but he insists that it wasn't. He just packed in the job and went climbing - in Central America, South America and Pakistan, as well as Alaska. His journey to Iraq, he says, was born of anger and frustration; it was not a calculatedly political act. "I did it for more personal reasons," he explains. "I felt if I went and did this, I'd be able to come home and sleep a little bit better at night." He was wrong about that.

He had seen that first trip in the winter of 2003 as a one-off, but when he realised he could probably earn enough to live through his journalism he decided to go back. The fact that the security situation was deteriorating and
that other journalists were pulling out increased the marketability of his on-the-spot reports, but also underlined the personal risks. Did he worry about the dangers? "By then I felt like I really wanted to stay in there and cover as much of the story as I could. You get into the story and you want to stay on it. It had its limits, though, and I didn't feel like I'd be able to stay in indefinitely."

He entered Iraq for the second time in April 2004, on the very day that Falluja, the town 70km west of Baghdad that became the focal point of the battle between US forces and Iraqi fighters, was being sealed off. "We immediately started hearing these horrible stories of what was happening there," he says. "I had a chance to go in and was really on the fence on whether I should do it or not, because I knew it was pretty crazy. But it seemed like we had a reasonable chance of going in safely, so I decided to take it. I ended up reporting for a couple of days from this makeshift clinic, and saw women, kids and some men being brought in who were all saying the same thing: the US pushed in [to Falluja] as far as they could and then just lined up snipers and started shooting into the city. There was no water, no electricity, medical workers were being targeted. It was a turning point for me."

By now, Jamail was filing his reports predominantly for the Inter Press Service, an agency based in Rome that sets out to "give a voice to the voiceless" and promote a new global order based on equality, democracy and justice. It is reporting, but reporting with a purpose, a clear agenda. So is it objective? Can someone who goes to Iraq convinced that the war is wrong and being fought for control of oil and strategic power offer unbiased reporting?

"Objective journalism is a myth," says Jamail. "Going into Iraq, I felt it was really important to read up on the history, find out what is the US security strategy, what is US foreign policy. Only then can you understand the facts and the nature of the US's historical involvement in Iraq. If I'm guilty of something, I was guilty of going into it looking at it through that lens, as opposed to those who were looking at it through the lens of anonymous briefings from Bush administration officials. Any journalist going into a war zone is going to be looking through a certain type of lens. It's a myth that you go in without opinions on the situation, or that you won't feel emotions and that nothing that happens is going to affect how you report on it. I don't buy that. I just don't think it's humanly possible."

He immediately qualifies that, however, by saying that he was not so blinkered that he made every fact and opinion he encountered fit his preconceived view. "When I came across Iraqis who were happy that Saddam was gone - and there were plenty, especially seven months into the occupation, before things had really started to degrade rapidly - I said so. I did run into things that challenged my preconceptions. I would from time to time run into a soldier who really believed in the mission. Early on, I met plenty of Iraqis who were glad the Americans were here, were still hopeful and wanted to give them some time, and I wrote about that."

In the introduction to his book, he quotes the story of an indigenous Canadian hunter who was called to give evidence at an inquiry into a planned dam that would flood his homeland and destroy his traditional way of life. The hunter was asked to swear on the Bible that he would tell the truth, but he had never seen a Bible and wondered how this miraculous truth-telling instrument worked. "He spoke with the translator at length," writes Jamail, "and finally the translator looked up at the judge. 'He does not know whether he can tell the truth. He says he can tell only what he knows.'"

I take it that is how Jamail sees his own role: to give his view, to write down what he sees, to filter what he discovers at first hand through the knowledge he has gained from reading official documents; to tell what he knows rather than claim to be relaying some almost metaphysical "truth", arrived at by
being perfectly objective. He sees the war in Iraq as the direct consequence of the stated national security strategy of building a worldwide network of US military bases and "projecting power". Talk of withdrawal from Iraq, he says, is a case of "putting the cart before the horse"; the whole strategy has to be rethought first. Iraq, in his view, is just a symptom of an endemic illness.

What this role as an avowedly anti-war journalist means, however, is that Jamail's political opponents can write him off as a propagandist. American TV networks have largely ignored him and his book. Even as the public mood has turned against the war, the mainstream media have not been able to disengage themselves from their view that, in time of war, the commander-in-chief and the boys in the field should be supported.

"I certainly get accused of being an activist, but I don't consider myself an activist," he says. "I've never done any kind of activism or organising. My response to my critics is to say, 'Tell me which of my facts you dispute and I'll give you my sources.' I ask people, 'Be specific.' If you want to attack my personality that's fine, but if you want to attack my work and my information, then tell me which of my stories you have a problem with and I'll happily give you my sources. I give talks in the US and people accuse me of being a conspiracy theorist, but I say, 'No, it's very rational, read these documents.'"

Jamail's Lebanese name doesn't help when he tries to argue that, while trying to fill the silence on the Iraqi side, he remains committed to reporting what he sees and telling what he knows. "One time I was on this rightwing radio programme, and the guy started out trying to describe me: 'Dahr Jamail, you're a Muslim, aren't you?' 'No. Would it matter if I was? But no, I'm not.' 'Where are you from, Dahr?' 'Anchorage, Alaska.' It didn't go real well for him. I didn't even have a Middle-Eastern accent."

Jamail made two further trips to Iraq, but hasn't been back since early 2005. The danger was now too great, and he was suffering from post-traumatic stress disorder. "Having never reported in a war zone before, I was ignorant about PTSD," he says. "I assumed that journalists didn't get it. I thought you had to be a combat soldier to get it. When I got home after my fourth trip, I started having trouble sleeping. I was constantly thinking about Iraq, getting random visions of the times when I would go into morgues, and feeling guilty that I could leave the country but the friends I had made there couldn't. I just felt numb a lot of the time. All of that put together made me realise that this was not the same guy that went over there, and that I needed some help. I took counselling, and still do it off and on when necessary."

When he returned to the US after his fourth visit to Iraq, he decided it was time to digest his experiences. He attended a session of the World Tribunal on Iraq in Rome and, rather like the Canadian hunter, reported what he had seen in the eight months he had spent in the country. He told of Iraqis who had given him accounts of being tortured, of towns collectively punished by being deprived of electricity, water and essential medical supplies, and of ambulances being shot at by US soldiers. "With 70% unemployment, a growing resistance and an infrastructure in shambles," he concluded, "the future for Iraq remains bleak as long as the failed occupation persists."

Jamail also embarked on his book - part reportage, part catharsis - and this summer plans to write another, this time on resistance to the war within the US military, based on the stories of soldiers he has met who engaged in sabotage and fake patrols (called "search and avoid" missions) to hamper the war effort. Then he plans to return to the Middle East and maybe even to Iraq, if the security situation allows him at least some degree of freedom to report. The return to the mountains will have to wait; his heart now is in the desert.