The Federal Security Service (FSB) which has led the investigation, has continuously violated national and international standards of criminal procedure and appears to be more concerned in obtaining Aleksandr Nikitin's conviction than in establishing truth through fair judicial determination.

'Aleksandr Nikitin has been acquitted and proven innocent of espionage. Attempts to re-open the case after a four year investigation and a Supreme Court verdict undermines Russia's judiciary and sends a message to the environmental movement that freedom of expression will not be tolerated,' the organisation said.

The former naval officer was accused in 1996 of leaking state secrets after writing about the environmental consequences of nuclear submarines for Bellona, a Norwegian environmental organisation.

Amnesty International and the Russian human rights movement have campaigned against the persecution of Aleksandr Nikitin, who was merely exercising his right to freedom of expression.

The organisation is urging the Supreme Court to throw out the appeal and close the case once and for all.

'The FSB wants to re-open a case that should never have been opened in the first place,' Amnesty International said. 'The FSB appears to be desperate to silence Aleksandr Nikitin and send a message to other activists they should not criticize the government.'