The grotesque revelations of abuse at Abu Ghraib were a kind of epiphany for Fernando Botero. Until then the Colombian artist had used his talent to present an idealised version of the world, one most commonly populated by friendly fat people, as opposed to mean-hearted thugs. Indeed, he once told an interviewer that he thought displays of genuine hatred had no place in art.

"All my life I've believed that a painter should concentrate on gentle subject matters," the 73-year-old Colombian artist tells me when we meet at his studio in Paris. "But I changed my mind with Abu Ghraib. First of all I was shocked, then I felt very angry and wanted to do something about it. Painting has the power to point the finger at what happened. Look at Guernica, that's an event that would probably be forgotten by now if it was not for Picasso."

Compared with the paintings that Botero exhibited in Bogotá early last year commemorating Colombia's 40 years of civil strife, the new work, some of it which stands in the downstairs studio of his Paris atelier, makes a very different kind of statement. Any ambiguity present in a Colombia-set painting such as "The Procession", where the identities and affiliations of the victims at a mass funeral are unclear, is totally absent from the Abu Ghraib tableaux, where torturer and tortured in the Iraqi prison are clearly delineated.

"In Colombia there is violence but this violence is born out of ignorance, lack of education and social injustice," he says. "What happened with Abu Ghraib disgusted me far more because it was carried out by a country which presents itself as a model of compassion and civilisation. It's barbaric to torture people and it was done in such a perverse way because it was not only physical but psychological torture."

So far Botero has completed 16 oil paintings and 40 drawings and has no intention of abandoning his subject just yet. "I still have a lot of things to say about this," he mutters. The three large canvases in Botero's studio are about as close to expressionism as he cares to venture. Full of vivid primary colours, they are reminiscent of the work of socially conscious Mexican muralists such as José Clemente Orozco and Diego Rivera, artists who fascinated the young Botero growing up in Medellín.

"When I did my first paintings as a young man they were very dramatic, I was very influenced by Orozco, depicting coffins and cemeteries and things like that," he says. "So in a way I've come back to something I did many, many years ago. As an artist you have two responsibilities: the artistic responsibility to create an important painting and the subject matter."

The first thing one notices about the Abu Ghraib tableaux is that the often naked bodies of the tortured, while inflated in typical Botero style, are not the plump prelates of old but muscular he-men, all the more pitiful for their trussed-up impotence. Their torturers wear rubber gloves to avoid touching them. Rubber batons and snarling attack dogs feature prominently. In many of the paintings the Iraqi victims are dressed in women's underwear and are being forced to engage in simulated homosexual acts.

Botero's emphasis on sexual forms of humiliation was informed by Seymour Hersh's piece in the New Yorker, "Torture at Abu Ghraib", which revealed the systemic scale of the torture at the prison. Afterwards Botero found digital images published on the internet of the kind of mistreatment favoured by the US military at Abu Ghraib. But once down to work, Botero put all that aside, preferring as is his wont, to draw and paint from memory and use his imagination.

"The artistic possibilities, leaving aside the anger one feels about what happened, were great because of the absurdity of the situation," he says. "When you see bodies piled up into a pyramid there is a plasticity there. It sounds terrible but it's the truth. There's a fresco by Giotto called The Massacre of the Innocents, in which you see a pile of dead children. When I saw the photo of these prisoners in Abu Ghraib stacked one on top of the other it made me think of Giotto. It's unbelievable but in this horror one could find artistic beauty."

Botero does not plan on selling any of the Abu Ghraib tableaux, as he says he does not want to profit from people's suffering. Instead he is thinking about donating them to galleries in Europe or the US.

Before that happens, he will embark on a round of exhibitions beginning next month in Rome, then moving on to Athens. In Rome, Botero will become the first living artist to exhibit in the Palazzo Venezia. On display will be 180 of Botero's tableaux done over the last 15 years, including 10 paintings and 30 drawings from the Abu Ghraib series. Offers have also been made by museums in Hanover and Baden Baden to hold exhibitions focusing exclusively on the Abu Ghraib work.

So far there have been no invitations from the US, the place where Botero is most keen to exhibit his new work. Ironically this lack of interest harks back to when Botero first moved to New York from Colombia in 1960. It was the beginning of the pop art movement and Botero's inflated figurative style was frequently cold-shouldered by the fashionable galleries.

Nevertheless the Colombian stayed, making New York his home for the next 13 years, "working, always working". The turning point came when a German museum director visited New York in 1969 and invited Botero to hold several exhibitions in Germany. After that the world's top galleries started to show an interest in his work. In 1992, Sotheby's sold Botero's The House of Arias Twins for $1.5m, the highest price paid for the work of a living Latin American artist. Botero now divides his time between Colombia, Paris, New York and Pietresanta in Italy, where he sculpts.

Despite his initial struggles, Botero's New York experience does not seem to have left him with a sour taste. "There's no doubt that following a different path to everyone else has been very important to my development as an artist," he explains. "In a way I believe I owe my good health to this independence because I saw so many artists move to New York in the 1960s and immediately get sidetracked by the pop art movement." Indeed, he appears to have a deep affection for the US. He enjoys visiting a son who lives in Miami and mentions in passing that many of his original ideas about art were inspired by reading the books of the American art historian Bernard Berenson.

Any suggestion that Botero is finally getting his own back on the US following his rejection in New York early in his career seems wide of the mark. Instead he wonders about the traditional disinclination of North American artists to tackle the same subject matter; he points out that are no famous paintings depicting the war in Vietnam, just as there are none of Abu Ghraib. Perhaps it's too early, or perhaps American artists believe, as Botero once did, that displays of hatred in art are incongruous with painting. Or perhaps they just don't have the Colombian's experience.

When I ask him if he would have been able to paint these tableaux of Abu Ghraib 30 years ago, Botero replies: "No, I don't think so. My imagination is more flexible now and I'm better on a technical level. So 30 years ago, no, but I would paint it even better 30 years from now."