In the John Singer Sargent room of the Imperial War Museum, next to Sargent's harrowing painting of gassed first world war soldiers, are giant drawings where 'crowds of people migrate endlessly through a deserted landscape towards an unknown destination'. The title of this exhibition is Displaced, and in the words of its curator it 'pays contemporary tribute to the endurance of civilians in the face of chemical attack, forced migration, mass killing and deep suffering'.
The artist is Osman Ahmed, born in 1962 in Sulaymaniyah, northern Iraq. Refusing to join the 1980-1988 war between Iraq and Iran, he ran off to join the Kurdish partisans in the mountains - the peshmerga militia of the left-wing Patriotic Union of Kurdistan.
'I was a peshmerga but never held a gun, just a pen, and did the cooking and teaching children. I told the fighters "I cannot kill" and the PUK accepted it,' he says. 'While I was in the mountains I saw Goya's drawings, The Disasters of War, and determined to travel to Poland to study graphics.'
Crossing the Iranian border, Osman managed two days in Tehran, where he caught his first dazzling sight of modernism - Picasso and Chagall on view in the Shah's old palace - before being arrested and sent to jail. Iran's prison authorities wanted propaganda paintings of Ayatollah Khomeini and the Aqsa mosque in Jerusalem. The artist disguised his abilities to cover his refusal: 'I let them think I was mad; they let me carve in soap, and paint over religious postcards.'
Among the surviving pieces from that time are traumatic faces, the bright paint scratched so that parts of the underlying card shows through. In the middle of one of those howling heads, like a window onto another world, a blue square remains from the original photo of a pious Shia boy, binding a text to his forehead.
Drawing the Anfal
'I went back to the peshmerga for two years, then crossed the Turkish border from Iran with a false passport, was arrested again and spent time in two Turkish prison camps,' says Ahmed. 'As I came back to Kurdistan through the mountains, I saw a Hunter helicopter dropping something that made a different noise from a bomb. We went to help a shepherd, and found it was nerve gas. For several days I was blind, and my legs swelled up so I could not walk.'
The Anfal had started - Saddam Hussein's genocidal attack against the rebellious Kurds. Tens of thousands of people were displaced. Amnesty International estimates the 'disappeared' at more than 100,000. The experience is traced by Ahmed's curling lines on paper.
Here are people so thickly crowded and so distantly seen that their forced march resembles a cloud of smoke, their compressed mass becomes the mouth of a giant grave. These pictures slide between portrait and abstract, sometimes directly recording horror and sometimes literally drawing back from something too traumatic to tell. The latest images remind me of Mark Rothko, who found during the Holocaust that one repeated, varying shape - based on a mass grave he had seen in his Latvian childhood after a pogrom - was the way he could best commemorate the countless dead.
Under the Anfal, Osman was again displaced into Iran. He spent two years in a refugee camp, where he was allowed to paint and teach and married a fellow artist. This time the Iranian authorities called him to do what he most wanted: to set up an international exhibition to prove to the world the crime that had destroyed Halabja. At the time Iraq, supported by the west, was claiming that the poison gas atrocity and razing of the rebel Kurdish town had been perpetrated by Iran.
First negotiating through his party to ensure that the exhibition would be independent - and in no way branded by Iran's pasdaran (revolutionary guards) - Ahmed created cards, which travelled all over the world. He and his fellow artists remained unable to get visas, and once the war was over Iran again put pressure on the Kurds.
Free for the first time
He travelled into Syria and exhibited his work in Damascus at just the moment Saddam Hussein had invaded Kuwait. PUK leader Jalal Talabani enabled Osman to leave at last to study his art, this time in Russia. But Iraqi agents and assassins were all over Moscow. He travelled once more - to London.
'For the first time in my life I could say I was Kurdish,' he says. 'I had no money - £27 a week - but I felt free. Free from worries about my family, the PUK, my country . . .
'I've worked as a bus driver, a waiter, on a market stall. I keep art apart from money. Art is life, my art is a document, not just something nice on a wall.'
'I still have a trauma; for long years it's stayed with me,' Ahmed continues. 'Watching the army come for the villagers, watching them driven out and knowing our forces were too few and weak to do anything to stop it.
'I keep working, keep looking - my work is what makes me human.'
One compelling pencil drawing shows a figure on fire, trailing clouds of graphite hair and smoke, emerging from a forest. The lines began with the exiled artist sketching the vertical punk-afro haircut on a fellow traveller on a London bus.
'I love line, and drawing. Line is a hero to me, to take out the emotions inside me.' Now this small, gently mannered and normally quiet man is speaking with the force and speed of red-hot lava. My pen skitters on the page trying to keep up, to do justice to his words.
'The Imperial War Museum is my first chance to be shown alongside the international riches of art, beside Sargent's picture of gas and what it does,' he goes on. 'We Kurds have always been in the shadow - we are friendly to others, to the problems of humanity, but they don't know about us.
'In the mountains we heard Radio London, Monte Carlo, radio stations everywhere. But there was no voice about us, as the army was coming to clean up the villages. That stays, that pain; all the countries around us knew and said nothing. We had to see people being taken away, we were too few to do anything. I could only record.
'My dream was to have the chance to tell our story in a very high place, to put it in a museum among the greatest artists. Ever since I was fascinated by Goya when I was in the mountains, I wanted to show genocide, to stop crimes against humanity everywhere in war. I try to add my voice on Darfur, Cambodia, Brazil [the extermination of indigenous people].
'When I was asked to draw in Tate Britain's After Turner show, one of his drawings of a Scottish mountain took me back to Kurdistan. It was great to be there - next to Turner! It was like being a survivor as a peshmerga, a victory as an artist recording genocide.'
Osman Ahmed: Displaced is at the Imperial War Museum, London, until 7 September. More of his work can be seen on his website at www.osmankader.com. His drawing after Turner's Mountain near Dunkeld can be seen at: http://tinyurl.com/6jkb73
Amanda Sebestyen curated Osman Ahmed in the group show
Strains of War at Greenwich Citizens' Gallery in 1992