Donets (Russia) (AFP) - Ukrainian airforce helicopter pilot Nadiya Savchenko on Tuesday blasted Russian prosecution 'lies' against her at the start of a trial over the murder of two journalists that has caused outrage in Kiev and the West.

Savchenko faces up to 25 years in prison for her role in the deaths of the two Russian reporters killed by mortar fire last summer in eastern Ukraine.

Her detention by Moscow has become a cause celebre in her crisis-wracked homeland after she said she was kidnapped by Russian special forces and smuggled across the border.

"It's lies, all of it from beginning to end," Savchenko told the court from the glass cage for defendants after the prosecution laid out its case.

"I was kidnapped from Ukrainian territory" the 34-year-old aviator, clad in a traditional Ukrainian blouse, told the court in Ukrainian.

"I never in my life shot at unarmed people, I'm a soldier not a murderer," she said, demanding to be cross-examined using a lie detector.

Savchenko is standing trial in the small southern Russian town of Donetsk, on the border with conflict-torn Ukraine, in a move her defence says is aimed at shielding the proceedings from the public eye.

She has spent over a year in custody in Russia during which she protested at her detention by going on hunger strike for more than 80 days. She was also elected in absentia to Ukraine's parliament last November.

Riot police armed with machine guns stood outside the court as snipers watched from the roof of a nearby apartment block.

Many of the courtroom's public seats were occupied by Cossack militiamen, but most media were barred and made to watch the trial via video-link from an adjoining room.

"Everyone in this room understands very well this is not a case, it's a piece of rubbish," the defiant pilot said in her opening remarks to the court.

She reiterated her innocence as relatives of the killed journalists testified in the hearing via a video link.

"I didn't kill your son. I'm very sorry it happened," she told the father of late reporter Anton Voloshin.

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Three representatives from the European Union, a Ukrainian consul based in Rostov-on-the-Don, and Savchenko's sister Vira, who has actively campaigned for her release, were among those who attended the hearing.

- 'Prepared for any sentence' -

The United States has described Savchenko as a "hostage" in Moscow's scrap with Ukraine and called for her to be released, along with several other Ukrainians held in Russia.

Kiev and the West insist Moscow has sent troops and arms across the border to fuel a separatist conflict that has claimed almost 8,000 lives since April 2014, allegations that Moscow vehemently denies.

Last month a Russian court sentenced Ukrainian film director Oleg Sentsov to 20 years in jail on terror charges in a trial decried as "fatally flawed" by Amnesty International.

Lawyers for Savchenko have expressed little hope that she will receive a fair trial and have said she is bracing for a long jail term.

"Nadiya Savchenko has prepared herself for any sentence," one of her lawyers, Mark Feigin, told journalists.

"If there is even one chance to get her acquitted through the publicity round her, then we will use it."

Feigin said the next hearing would be September 29 and that the court could reach a verdict in November.

Earlier in the day a handful of Kremlin supporters demonstrated against Savchenko outside the court house.

"The aim of our picket is to support our justice system," said activist Alexei Mikhailovich.

He added he hoped Savchenko would "be sent to sunny Magadan," referring to the far eastern Russian city that served as a hub for labour camps in the Soviet era.