A Russian court on Wednesday acquitted a retired naval officer, Alexander Nikitin, who was charged with treason and espionage after revealing a pollution risk from abandoned nuclear submarines.

The St Petersburg city court threw out all the the accusations made against Mr Nikitin.

Judge Sergey Golets said the prosecution's charges were a violation of the Russian constitution, because the information Mr Nikitin revealed was only classified after he had been charged.

Verdict welcomed

He also said the investigation contained many procedural errors.

The Norwegian magazine that published Mr Nikitin's revelations, Bellona, welcomed the verdict.

"The acquittal of Alexander Nikitin means that the environmental movement in Russia may resume its important task of cleaning up the mess left after too many years of Cold War and economic failure," it wrote.

"It also means that the terror regime of the secret service may have come to an end, surpassed by the rule of law in Russia."

In a 1996 report for Bellona Mr Nikitin wrote about 52 abandoned nuclear submarines in a remote shipyard near Russia's border with Norway.

The Cold War-era submarines hold spent nuclear fuel that could leak, overheat or explode, he said.

Prosecutors with the Federal Security Service - one of the successors of the KGB - had demanded that Nikitin be sentenced to 12 years in a labour colony and have his property confiscated.

They said they would appeal against the court's ruling.

No regrets

Mr Nikitin, 46, spent the first 10 months of the four-year legal battle in pre-trial detention at the Federal Security Service's prison in St Petersburg.

He appealed for charges to be dropped after a court ruled that prosecutors had insufficient evidence, and should prepare the case again - but his appeal was rejected by Russia's Supreme Court.

Mr Nikitin and Bellona said the information was not secret but came from public records, including school textbooks.

"If time turned back, I would do it all again," Mr Nikitin said.

He added that the verdict was "very good news for Russia".

Mr Nikitin's co-author, Igor Kudrik, said Russian environmentalists would have to overcome "the Nikitin effect", which made many of them afraid to speak out about nuclear pollution.

In 1996 Amnesty International declared Mr Nikitin a prisoner of conscience and described the case against him as "one of the most controversial criminal cases in Russia since the collapse of the Soviet Union".