The prize-winning writer and creator of Wallander was among those on board the Gaza flotilla. Here he shares his private diary of the events leading to his capture

Tuesday 25 May, Nice

It is five o'clock in the morning and I'm standing in the street waiting for the taxi that will take me to the airport in Nice. It's the first time in ages E and I have had some time off together. Initially we thought we'd be able to stretch it to two weeks. It turned out to be five days. Ship to Gaza finally seems to be ready to set off and I'm to travel to Cyprus to join it, as arranged.

As instructed, I've limited my luggage to a rucksack weighing no more than 10 kilos. Ship to Gaza has a clearly defined goal: to break Israel's illegal blockade. After the war a year ago, life has become more and more unbearable for the Palestinians who live in Gaza. There is a huge shortage of the bare necessities for living any sort of decent life.

But the aim of the voyage is of course more explicit. Deeds, not words, I think. It's easy to say you support or defend or oppose this, that and the other. But only action can provide proof of your words.

The Palestinians who have been forced by the Israelis to live in this misery need to know that they are not alone, not forgotten. The world has to be reminded of their existence. And we can do that by loading some ships with what they need most of all: medicines, desalination plants for drinking water, cement.

The taxi arrives, we agree a price – extortionate! – and drive to the airport through empty, early morning streets. It comes to me now that I made my first note, there in the taxi. I don't remember the exact words, but I'm suddenly disconcerted by a sense of not quite having managed to register that this is a project so hated by the Israelis that they might try to stop the convoy by violent means.

By the time I get to the airport, the thought has gone. On this point, too, the project is very clearly defined. We are to use non-violent tactics; there are no weapons, no intention of physical confrontation. If we're stopped, it ought to happen in a way that doesn't put our lives at risk.

Wednesday 26 May, Nicosia

It's warmer than in Nice. Those who are to board the ships somewhere off the coast of Cyprus are gathering at Hotel Centrum in Nicosia. It's like being in an old Graham Greene novel. A collection of odd people assembling in some godforsaken place to set off on a journey together. We're going to break an illegal blockade. The words are repeated in a variety of languages. But suddenly there's a great sense of uncertainty.

The ships are late, various problems have arisen, the coordinates still haven't been set for the actual rendezvous. The only thing that's certain is that it will be out at sea. Cyprus doesn't want our six ships putting in here. Presumably Israel has applied pressure.

Now and then I also note tensions between the various groups that make up the leadership of this unwieldy project. The breakfast room has been pressed into service as a secretive meeting room. We are called in to write details of our next of kin, in case of the worst. Everyone writes away busily. Then we are told to wait. Watch and wait. Those are the words that will be used most often, like a mantra, in the coming days. Wait. Watch and wait.

Thursday 27 May, Nicosia

Wait. Watch and wait. Oppressive heat.

Friday 28 May, Nicosia

I suddenly start to wonder whether I may have to leave the island without getting onto a ship. There seems to be a shortage of places. There are apparently waiting lists for this project of solidarity. But K, the friendly Swedish MP, and S, the Swedish female doctor, who are travelling with me help keep my spirits up. Travel by ship always involves some kind of bother, I think. We carry on with our task. Of waiting. Watching and waiting.

Saturday 29 May, Nicosia

Suddenly everything happens very quickly. We are now, but of course still only maybe, to travel sometime today on a different, faster ship to the point out at sea where the coordinates meet, and there we will join the convoy of five other vessels that will then head as a single flotilla for the Gaza Strip.

We carry on waiting. But at about 5pm the port authorities finally give us permission to board a ship called the Challenge, which will take us at a speed of 15 knots to the rendezvous point, where we will transfer to the cargo ship Sophia. There are already lots of people aboard the Challenge.

They seem a bit disappointed to see the three of us turn up. They had been hoping for some Irish campaigners who have, however, suddenly given up the idea and gone home. We climb aboard, say hello, quickly learn the rules. It's very cramped, plastic bags full of shoes everywhere, but the mood is good, calm. All the question marks seem to have been ironed out now. Soon after the two diesel engines rumble into life. We're finally underway.

23.00

I've found a chair on the rear deck. The wind is not blowing hard, but enough to make a lot of the passengers seasick. I have wrapped myself up in blankets, and watch the moon cast an illuminated trail across the sea. I think to myself that solidarity actions can take many forms. The rumbling means there is not a lot of conversation. Just now, the journey feels very peaceful. But deceptively so.

Sunday 30 May, at sea, south-east of Cyprus, 01.00

I can see the glimmer of lights in various directions. The captain, whose name I never manage to learn, has slowed his speed. The lights flickering in the distance are the navigation lights of two of the other ships in the convoy. We are going to lie here until daylight, when people can be transferred to other vessels. But I still can't find anywhere to sleep. I stay in my wet chair and doze.

Solidarity is born in dampness and waiting; but we are helping others to get roofs over their heads.

08.00

The sea is calmer. We are approaching the largest vessel in the flotilla. It's a passenger ferry, the "queen" of the ships in the convoy. There are hundreds of people on board. There has been much discussion of the likelihood of the Israelis focusing their efforts on this particular ship.

What efforts? We've naturally been chewing that over ever since the start of the project. Nothing can be known with any certainty. Will the Israeli navy sink the ships? Or repel them by some other means? Is there any chance the Israelis will let us through, and repair their tarnished reputation? Nobody knows. But it seems most likely that we'll be challenged at the border with Israeli territorial waters by threatening voices from loudspeakers on naval vessels. If we fail to stop, they will probably knock out our propellers or rudders, then tow us somewhere for repair.

13.00

The three of us transfer to the Sophia by rope ladder. She is a limping old cargo ship, with plenty of rust and an affectionate crew. I calculate that we are about 25 people in all. The cargo includes cement, reinforcement bars and prefabricated wooden houses. I am given a cabin to share with the MP, whom I view after the long days in Nicosia more and more as a very old friend. We find it has no electric light. We'll have to catch up on our reading some other time.

16.00

The convoy has assembled. We head for Gaza.

18.00

We gather in the improvised dining area between the cargo hatches and the ship's superstructure. The grey-haired Greek who is responsible for security and organisation on board, apart from the nautical aspects, speaks softly and immediately inspires confidence. Words like "wait" and "watch" no longer exist. Now we are getting close. The only question is: what are we getting close to?

Nobody knows what the Israelis will come up with. We only know that their statements have been menacing, announcing that the convoy will be repelled with all the means at their disposal. But what does that mean? Torpedoes? Hawsers? Soldiers let down from helicopters? We can't know. But violence will not be met with violence from our side.

Only elementary self-defence. We can, on the other hand, make things harder for our attackers. Barbed wire is to be strung all round the ship's rail. In addition, we are all to get used to wearing life jackets, lookouts are to be posted and we will be told where to assemble if foreign soldiers come aboard. Our last bastion will be the bridge.

Then we eat. The cook is from Egypt, and suffers with a bad leg. But he cooks great food.

Monday 31 May, midnight

I share the watch on the port side from midnight to 3am. The moon is still big, though occasionally obscured by cloud. The sea is calm. The navigation lights gleam. The three hours pass quickly. I notice I am tired when someone else takes over. It's still a long way to anything like a territorial boundary the Israelis could legitimately defend. I should try to snatch a few hours' sleep.

I drink tea, chat to a Greek crewman whose English is very poor but who insists he wants to know what my books are about. It's almost four before I get to lie down.

04.30

I've just dropped off when I am woken again. Out on deck I see that the big passenger ferry is floodlit. Suddenly there is the sound of gunfire. So now I know that Israel has chosen the route of brutal confrontation. In international waters.

It takes exactly an hour for the speeding black rubber dinghies with the masked soldiers to reach us and start to board. We gather, up on the bridge. The soldiers are impatient and want us down on deck. Someone who is going too slowly immediately gets a stun device fired into his arm. He falls. Another man who is not moving fast enough is shot with a rubber bullet. I think: I am seeing this happen right beside me. It is an absolute reality. People who have done nothing being driven like animals, being punished for their slowness.

We are put in a group down on the deck. Where we will then stay for 11 hours, until the ship docks in Israel. Every so often we are filmed. When I jot down a few notes, a soldier comes over at once and asks what I am writing. That's the only time I lose my temper, and tell him it's none of his business. I can only see his eyes; don't know what he is thinking. But he turns and goes.

Eleven hours, unable to move, packed together in the heat. If we want to go for a pee, we have to ask permission. The food they give us is biscuits, rusks and apples. We're not allowed to make coffee, even though we could do it where we are sitting. We take a collective decision: not to ask if we can cook food.

Then they would film us. It would be presented as showing how generously the soldiers had treated us. We stick to the biscuits and rusks. It is degradation beyond compare. (Meanwhile, the soldiers who are off-duty have dragged mattresses out of the cabins and are sleeping at the back of the deck.)

So in those 11 hours, I have time to take stock. We have been attacked while in international waters. That means the Israelis have behaved like pirates, no better than those who operate off the coast of Somalia. The moment they start to steer this ship towards Israel, we have also been kidnapped. The whole action is illegal.We try to talk among ourselves, work out what might happen, and not least how the Israelis could opt for a course of action that means painting themselves into a corner.

The soldiers watch us. Some pretend not to understand English. But they all do. There are a couple of girls among the soldiers. They look the most embarrassed. Maybe they are the sort who will escape to Goa and fall into drug addiction when their military service is over? It happens all the time.

18.00

Quayside somewhere in Israel. I don't know where. We are taken ashore and forced to run the gauntlet of rows of soldiers while military TV films us. It suddenly hits me that this is something I shall never forgive them. At that moment they are nothing more to my mind than pigs and bastards.

We are split up, no one is allowed to talk to anyone else. Suddenly a man from the Israeli ministry for foreign affairs appears at my side. I realise he is there to make sure I am not treated too harshly. I am, after all, known as a writer in Israel. I've been translated into Hebrew. He asks if I need anything.

'My freedom and everybody else's,' I say. He doesn't answer. I ask him to go. He takes one step back. But he stays.

I admit to nothing, of course, and am told I am to be deported. The man who says this also says he rates my books highly. That makes me consider ensuring nothing I write is ever translated into Hebrew again.

Agitation and chaos reign in this "asylum-seekers' reception centre". Every so often, someone is knocked to the ground, tied up and handcuffed. I think several times that no one will believe me when I tell them about this. But there are many eyes to see it. Many people will be obliged to admit that I am telling the truth. There are a lot of us who can bear witness.

A single example will do. Right beside me, a man suddenly refuses to have his fingerprints taken. He accepts being photographed. But fingerprints? He doesn't consider he has done anything wrong. He resists. And is beaten to the ground. They drag him off. I don't know where. What word can I use? Loathsome? Inhuman? There are plenty to choose from.

23.00

We, the MP, the doctor and I, are taken to a prison for those refused right of entry. There we are split up. We are thrown a few sandwiches that taste like old dishcloths. It's a long night. I use my trainers as a pillow.

Tuesday 1 June, afternoon

Without any warning, the MP and I are taken to a Lufthansa plane. We are to be deported. We refuse to go until we know what is happening to S Once we have assured ourselves that she, too, is on her way, we leave our cell.

On board the plane, the air hostess gives me a pair of socks. Because mine were stolen by one of the commandos who attacked the boat I was on.

The myth of the brave and utterly infallible Israeli soldier is shattered. Now we can add: they are common thieves. For I was not the only one to be robbed of my money, credit card, clothes, MP3 player, laptop; the same happened to many others on the same ship as me, which was attacked early one morning by masked Israeli soldiers, who were thus in fact nothing other than lying pirates.

By late evening we are back in Sweden. I talk to some journalists. Then I sit for a while in the darkness outside the house where I live. E doesn't say much.

Wednesday 2 June, afternoon

I listen to the blackbird. A song for those who died.

Now it is still all left to do. So as not to lose sight of the goal, which is to lift the brutal blockade of Gaza. That will happen.

Beyond that goal, others are waiting. Demolishing a system of apartheid takes time. But not an eternity.

Copyright Henning Mankell. This article was translated by Sarah Death