LONDON (Reuters) -Russian physicist Anatoly Maslov was convicted of treason and sentenced to 14 years in a penal colony on Tuesday in the latest of several cases against experts working on the science underpinning Russia's development of hypersonic missiles.

White-haired Maslov, 77, stood in a glass box in the St Petersburg courtroom and listened attentively without showing emotion, as the judge read the verdict after a trial that was closed to the press. He had protested his innocence.

Maslov is one of three scientists from the same Siberian institute, all specialists in hypersonics, who have been arrested since 2022 on treason charges. The other two, Alexander Shiplyuk and Valery Zvegintsev, are awaiting trial.

The trio, and a number of other scientists accused in similar cases, had conducted theoretical work in areas relevant to the development of hypersonic missiles - cutting-edge weapons capable of carrying payloads at up to 10 times the speed of sound to punch through air-defence systems.

President Vladimir Putin has said repeatedly that Russia is a world leader in these weapons, which it has acknowledged using in the Ukraine war.

Lawyer Yevgeny Smirnov of Pervy Otdel (First Department), an association that specialises in defending people in cases of treason and espionage, said the charges against all the accused scientists were similar - divulging information considered a state secret while participating in an international conference or research.

"Any conviction against Maslov is a gross violation of the law," he said. "I am sure that Maslov is not guilty of the acts accused of him and is a victim of the policies of the Russian authorities."

SHOCKED BY SENTENCE

Maslov's lawyer Olga Dinze told reporters her client, who has serious heart problems, was shocked by the sentence but was "holding firm" and would appeal.

She described him as a man who lived modestly and had dedicated his life to Russian science, turning down numerous invitations to leave the country and join a western university.

In a rare open letter published last year, colleagues at the Siberian institute said Maslov, Shiplyuk and Zvegintsev were innocent and the scientific papers they had published or presented to international conferences had been vetted to ensure they did not include restricted information.

They said the cases were having a chilling effect on Russian academia and making it impossible for scientists to do their jobs.

In response, the Kremlin said at the time that the men faced "very serious accusations" and their cases were a matter for the security services.

Maslov's lawyer Dinze said Maslov had come under investigation after a defendant in another case testified against him in return for a shorter sentence of seven years.

She was apparently referring to the jailing of Alexander Kuranov, another scientist in the same field, who was sentenced last month.

Dinze said the spate of arrests of top Russian academics by the FSB security service was regretful and ironic at a time when Putin was speaking of the need to invest in Russian science.

"Maybe the right hand doesn't know what the left hand is doing," she said.

Smirnov of Pervy Otdel told Reuters: "It is obvious that the persecution of scientists is an exclusively political step by the Russian authorities, by which they seek to show that intelligence services around the world are trying to steal the secrets of Russian weapons."

Smirnov said the detained scientists were not working directly on weapons, but studying physical processes associated with high speeds.

The so-called secrets they had passed on were "openly published and available to anyone", he said.

(Reporting by Mark TrevelyanEditing by Bernadette Baum)

By Mark Trevelyan