When Sofi Oksanen read the work of renowned Croatian writer Slavenka Drakulic, about the mass rape of women during the war in Bosnia, she was shocked.

The first time I met Oksanen, who is now an international publishing sensation herself, she recalled how young she was during that war.

"Suddenly, for me, a woman's body became a metaphor for an occupied country and the use of sexual violence, be it in Europe, Africa or the Middle East today," she said. Discovering that there were concentrations camps, in Europe, where rape was routinely committed while she was growing up in Finland, she wondered how it was that the world turned away.

That question still haunts Oksanen's work as her fourth novel, When The Doves Disappeared, comes out here next month, after being published in Finland and Sweden in 2012, where it soared to No 1, receiving ecstatic reviews.

In this, the third of a quartet of books exploring occupation and colonialism, the 38-year-old, who has a Finnish father and an Estonian mother, writes again about Estonia, one of the smallest of the Baltic states, shifting the story between 1941-44 and 1963-66. The country was occupied by the Soviet Red Army, then the Nazis, then the USSR again. In this tragically beautiful, densely detailed novel, Oksanen returns to the theme of the woman's body as a metaphor for political occupation, while her characters attempt desperately to cling to their humanity.

In Finnish the title, which refers to German soldiers capturing and eating the birds, is loaded with meaning; the same word means "doves", "pigeons" and "vipers". The novel is told primarily through the members of one family. Roland is with the resistance. His cousin, Edgar, creates stories of heinous Nazi crimes for Soviet propaganda while constantly reinventing himself. His despairing wife, Juudit, becomes the mistress of an SS-Haupsturmfuhrer. Edgar watches as she is caressed by her lover: "in that touch was all the love in the world, everything gentle and precious." The sight eats through him "like deadly poison".

Once again in Oksanan's oeuvre, a woman's body becomes a symbol of occupation by a hostile force, although Juudit is willingly complicit in the affair. There were Estonian women who had sexual relationships with Nazis, says Oksanen. "We don't know much about the collaborators, male or female, and we know even less about their families." She spoke to many people about the war years - "in Estonia you have to rely on oral history because there is no official collective memory" - and they all "knew" someone who collaborated or was involved sexually with a Nazi. "Nobody was willing to admit, 'I had an affair with a German.' It was always someone else, or 'My grandfather knew someone.' Reading between the lines, however... And that is how I want people to read my books, to understand powerful metaphors, to read between the lines because I write between the lines."

Her research ranged from newspaper archives and the labyrinthine structure of the security services to old telephone directories. "They name streets so I was able to create a map of the capital Tallinn during those years." She also researched Edgar Meos, an Estonian fabulist and forger, who fabricated Soviet propaganda, claiming to be a former pilot trained by the RAF. He is the mendacious model for sly, secretive Edgar in her novel.

As with all of Oksanen's previous books, sex and violence, fear, family secrets, betrayals, shame and loss, and the desperate need to survive are at the heart of this remarkable book, just as in her play, Purge, about Russia's long, cruel occupation of Estonia and sex traffickers from Vladivostok, who rape, abuse and hunt their victims, which she wrote after reading about the Bosnian conflict.

She turned that stage work into a 390-page novel (2008), because theatrical conventions silenced too many women's voices that she wanted to be heard. "Silence is a form of terror," she insists, adding that she has been touched by how people respond to her work. She is just back from a trip to Colombia, where she was thanked for breaking the silence of history. "I was amazed that I had so many Latin American readers, who really understood my work. I guess they bring their own history of living under dictatorships and memories of the 'disappeared' to it."

Purge has been hailed as a "masterpiece" and has also been filmed - "it's not bad... for a Finnish film". Readers tell her that they can't forget the book, that they dream about it long after finishing it. More than a million copies have been sold and Helsinki-based Oksanen became the first person in Finland to win the Finlandia and the Runenberg, named for the 19th-century national poet, of which she was the youngest ever recipient. She's also been awarded the Swedish Academy Nordic prize and France's Prix Femina.

In Finland, she has rock-star status - she certainly looks the part, with her black mane embellished with rainbow-coloured dreads that turn and twist about her head like the plotlines of so many novels waiting to be written. "I love your style," a man tells her in the Bloomsbury cafe, in London, where we're talking and drinking coffee.

Anyone who has read Oksanen certainly likes her literary style. As is evidenced in her semi-autobiographical debut novel, Stalin's Cows (2003), in which she examines Estonia's recent past, mother-and-daughter relationships, the female body and eating disorders from which she has suffered. Yet to be translated into English, it's the first of a quartet of novels. "I never planned to write four! I didn't even know I was going to write about Estonia; I thought I was too young at the time," she says, speaking charmingly accented English - learnt from watching British TV shows, such as Robin Hood, as a child.

"I was less than halfway with Stalin's Cows when I found I had so much more I wished to write about how history has been falsified. The book would have been enormous, unwieldy, complicated. There was so much material. I couldn't squeeze all that into one novel. I thought there might be two books, but..." She shrugs her shoulders, adding that she's working on the fourth in this quartet. "No. I can't say anything about it. I just need time to write it."

Happily, she found the time to write When The Doves Disappeared, which at 300 pages is just as harrowing and chilling a read as Purge, often told in gorgeous, lyrical language. She acknowledges that, in this country, many know little about Estonia and the mass executions and deportations the country suffered. In 1949, for instance, women and children and those who helped the Forest Brothers, who fought for freedom from Soviet rule, were sent to Siberia. (Her own grandfather was a partisan, but never spoke of it.) But how much did people know about Ukraine before Russia's stealthy invasion in 2014, she asks.

"I want my books to open windows - that is the power of fiction and art," she says, adding that President Putin declared Estonia an enemy state, in 2007, ironically, just as she began writing When The Doves Disappeared.

How has Estonia survived since gaining independence in 1991? There are many reasons, including Nordic money, she suggests. "But it's also because the Estonian language has miraculously survived many rulers and their attempts to destroy it." She warns that only a few months ago an Estonian soldier, working for the security services, was kidnapped by the Russians. "He's still alive but he was kidnapped simply to prove that they could kidnap an Estonian soldier."

Born in Jyvaskyla in central Finland, Oksanen spent her summers in Estonia, where her grandparents lived on a Soviet collective farm. Her aunt lived in Tallinn. She needed official permits for Oksanen and her mother to travel into the countryside, where the family had lived since the 17th century. Sometimes they were refused, so they would journey in secret, an awfully big adventure for a small girl who had begun keeping a diary at the age of six and who presented her first novel to her mother when she was ten-years-old.

"I have always known that writing was my thing," says Oksanen, who studied literature, then drama at Helsinki's Theatre Academy. Before she can complete her next book, however, she is writing the libretto for an opera commissioned by London's Royal Opera House from Finnish composer Kaija Saariaho. "She asked for me so it is quite a coup. It'll be kind of fun, although I think it's pretty brave of Kaija to trust me."

Finally, I ask Oksanen how she feels about the fact that when her books are translated into English, she is invariably described as a crime writer, "a female Stieg Larsson". Is she a writer lost in translation?

"That only happens in this country," she says. "I don't mind, but I don't write thrillers. My biggest literary influence is Kazuo Ishiguro. His novels are perfect." Has she read The Buried Giant? "He has a new book out? I didn't know that. Oh, I can't wait to read it!"

When The Doves Disappeared by Sofi Oksanen is published by Atlantic, priced £12.99