Moscow correspondent Andrew Harding: Nikitin has been harassed for three years

The man, Alexander Nikitin, was arrested in February 1996 by Russia's Federal Security Service (FSB), Russia's modernised and renamed security organisation, formerly known as the KGB.

He was charged with treason for spying and disclosing state secrets by providing information about nuclear contamination in Russia's Arctic military ports.

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Mr Nikitin, a former nuclear safety inspector for the Soviet and Russian ministries of defence, denies the charges against him.

He says all the information he provided was openly available and is confident he will be acquitted.

Human rights issue

The case has been closely watched by international human rights and environmentalist groups.

Protesters hung signs at the courthouse reading: "The Nikitin trial is a disgrace for Russia."

Mr Nikitin himself said he was concerned the FSB might try to rig the trial's outcome.

"We have no legal basis to dismiss the court staff, but at the same time we express concern that the FSB has the ability to influence the selection of the people's jurors," he said.

But he also said he was satisfied with the professional atmosphere at the courthouse.

"It is an entirely normal working environment. I think the judge is determined to maintain an exclusively working environment and that pleases me," he said during a break in the trial.

Run-up to the trial

In the years leading up to trial, Mr Nikitin and his lawyers say the Russian security services have shown contempt for the law, repeatedly changing their position and harassing him and his family.

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The federal security services have taken almost three years to compile their case against him.

He spent some of that time in prison, until appeals from Western governments led to his release.

Mr Nikitin has won numerous international human rights and environmental awards. Amnesty International declared him a prisoner of conscience - the first in Russia since physicist Andrei Sakharov.

International outrage

Siri Engeseth: "They have been harassing Nikitin"

Siri Engeseth, an official of the Norwegian environmental group Bellona, says the treatment of Mr Nikitin is outrageous and absurd.

"They have been harassing Nikitin constantly by telephoning him at night. They have hit him once by car, they cut his tyres," she says.

In Moscow, officials from the New York-based organisation Human Rights Watch described the case as "a litmus test of the government's commitment to civil society and the rule of law."

Also a former KGB agent, turned commentator, Konstantin Preobrazhensky, says the West should be watching closely.

"If Nikitin becomes guilty, it will mean the process of democratic reforms in Russia has been finished," Mr Preobrazhensky said.