CANNES, France (AFP) - US-Israeli Oscar winner Natalie Portman drew mixed reviews at the Cannes Film Festival on Friday for her directorial debut about a traumatic childhood during the birth of the state of Israel.

The world's top cinema showcase paired A Tale Of Love And Darkness, with another harrowing first feature, Hungary's Son Of Saul, which offered a shocking new depiction of the Holocaust.

While Portman's picture, in which she is also screenwriter and star, attracted only polite applause, Laszlo Nemes' relentless drama left a Cannes audience shattered.

It tells the story of Saul Auslaender, a prisoner at Auschwitz assigned to a Sonderkommando, a unit forced to help with the disposal of bodies from the gas chambers.

When he discovers a boy still alive among dozens of naked corpses, Saul believes the child is his long-lost son.

The boy's reprieve, however, is short-lived: a camp doctor finds him and snuffs out his breath with his hand. Saul then embarks on a mission to give the boy a proper burial and seeks a rabbi to read the Kaddish prayer for the dead.

While Steven Spielberg controversially pulled his punches in his Oscar-winning Schindler's List by turning a feared mass gassing of prisoners into a shower in a key scene, Nemes, 38, shows no such mercy.

The screams of the suffocating victims and the horror of the subsequent clean-up operation left many at the festival unwell, and the two-hour picture rarely lets up in its intensity, even as it transforms into an escape thriller.

Nemes lost several family members at Auschwitz-Birkenau camp in Nazi-occupied Poland, where some 1.1 million people, most of them European Jews, perished.

Nemes told AFP he "aimed to find a new way to show the hell of the extermination camps" because, in his view, "the subject has in general been treated in a way that is unsatisfying", by showing too much emotion and too little violence.

Early reviews were rapturous, with Peter Bradshaw of London's Guardian calling it "an astonishing debut film" of "extraordinary focus and courage".

US movie website Indiewire called it the "first sensation" among the 19 contenders for the festival's Palme d'Or top prize.

And British trade magazine Screen said the film powerfully showed "events that have, in the last three decades, been increasingly often represented in cinema, arguably to the point of devaluation".

FAMILIAR STORIES

Portman's first feature charts the birth of the state of Israel, where Holocaust survivors from across Europe sought refuge and a new lease of life.

Based on an international bestseller by Amos Oz, a writer and advocate of a two-state solution to the Israeli-Palestinian conflict, the film shot in sepia tones depicts a joyous patriotism among the early settlers that among some gives way to crushing disillusionment.

Portman, using her fluent Hebrew, plays Oz's mother Fania, a gifted storyteller who is haunted by the violence and loss she witnessed in her home country Ukraine, and stifled by the tedium of her new domestic life.

Portman, 33, was born in Jerusalem to a doctor father and an artist mother.

She said Oz's personal story set against the nation's transformation from a British mandate to an independent state had touched her deeply.

"I had heard many stories about my grandparents and their relationship to books and learning and to language and to Europe and Israel - it felt familiar and something I was interested in exploring," she said in production notes.

Portman said she had wanted to hand over the lead role to another actress but was unable to draw financing without her name on the marquee.

"No one would give me money, I tried for a few years, I couldn't get it. And they said, 'If you play it, we can find you some,'" said Portman, who drew the budget from several Israeli film funds.

Early reviews were muted.

Robbie Collin of Britain's Telegraph newspaper said on Twitter that Portman had escaped the fate of fellow actor-turned-director Ryan Gosling whose Lost River was savaged by Cannes critics last year, calling her movie "completely respectable".

But film industry bible Variety said it was a "drearily empathetic film" that "lacks whatever universality has made 'Tale' such an international phenomenon".