The defunct DFS agency bugged the Nobel laureate's phone and monitored his movements from 1967 after he moved to Mexico with his family. The authorities suspected the Colombian author of One Hundred Years of Solitude because of his leftist sympathies and friendship with Fidel Castro. Declassified documents published in the newspaper El Universal revealed the DSF kept a bulging file at least up until 1985, after which documents remain secret. It was era of the "dirty war" waged by rightwing Latin American governments against suspected subversives.

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The agency closely monitored the author's mediation between leftist movements and the French president, Francois Miterrand. It also kept tabs on Mexican writers such as Octavio Paz, who won the Nobel prize in 1990, and Salvador Novo.

Last week, the One Hundred Years of Solitude author's literary agent Carmen Balcells told a Chilean newspaper that she didn't think he would write anything else (somewhat galling for her, given that she also revealed Garcia Marquez represented 36.2% of her agency's income). Garcia Marquez's biographer, Gerald Martin, agreed, adding that this wasn't "too regrettable, because as a writer it was his destiny to have the immense satisfaction of having a totally coherent literary career many years before the end of his natural life".

But Garcia Marquez, father of magical realism, author of Love in the Time of Cholera and winner of the 1982 Nobel prize for literature, dismissed these comments yesterday when contacted by a Colombian paper. "Maestro, could you answer some questions for El Tiempo?" he was asked by the paper. "Call me later, I'm writing," the author known affectionately as "Gabo" responded tartly.

When he eventually agreed to answer two questions from El Tiempo, he put paid to the claims that his literary career was over. "Not only is it not true [that I won't return to writing], but the only thing I do is write," he said. Asked if he would publish more books, he responded that his job was "to write, not to publish". "I'll know when the cakes I am baking are ready," the 82-year-old concluded enigmatically.

Garcia Marquez's next book will be a love story, though his friend and fellow writer Plinio Apuleyo Mendoza said that the author was struggling to come up with a version that he was happy with. "He has four versions of it," Apuleyo said. "He told me that he was now trying to get the best from each of them."

Apuleyo, who co-wrote a book of conversations with García Marquez called The Smell of the Guava Tree in 1982, said the Nobel prizewinner had become hugely self-critical and demanding of himself. Two years ago, Garcia Marquez said: "I've stopped writing ... 2005 was the first year in my life that I didn't write a line."

He admitted, though, that his problem was one of enthusiasm rather than inspiration. "With all the practice I've got, I'd have no problems writing a new novel," he explained. "But people notice if you haven't put your heart into it." Apuleyo said Garcia Marquez described his year without writing as "a sabbatical", during which he had devoted his time to reading.

Mexican actor and producer Rodolfo de Anda says he has just acquired the rights to the long-forgotten screenplay and plans to start filming next year. Titled Frontera, the film was written before the 1967 novel One Hundred Years of Solitude turned Garcia Marquez into an international literary star known to most of the continent simply as Gabo.

"Nobody knew it existed, and the most surprising thing is that it is a Western. I don't think anybody knew he had written anything like that," De Anda told Mexican newspaper Reforma. De Anda says he first heard of Frontera as a young actor about 40 years ago when he was offered the part of the younger hitman. He assumed the screenplay had been written by Alcoriza, one of the giants of Mexico's cinematic golden age.

"When I finally bought the rights, about a month ago, I discovered the surprise that the story was not in fact by Alcoriza, but by Gabriel Garcia Marquez," De Anda said. He now plans to play the older partner, and is considering pursuing Mexican stars Gael Garcia Bernal or Diego Luna for the role of the upstart.