A Russian court has upheld a 12-year guilty verdict for treason against a physicist accused of passing secrets about hypersonic technology to the Netherlands, a Russian legal association said on Wednesday.

Valery Golubkin, a specialist in aerodynamics and the heat exchange of aircraft at a Moscow institute, was arrested in December 2020 and handed a guilty sentence in June 2023.

Russia's Supreme Court ordered a retrial in April, saying it had considered a complaint by Golubkin's defence.

The Pervy Otdel (First Department) legal group, which specialises in defending people in cases of treason and espionage, said investigators had found the scientist had passed secret information about hypersonic passenger airplanes to the Netherlands.

But it rejected such accusations.

"We know with certainty that there is no crime in Golubkin's actions, he acted strictly according to the law", said lawyer Yevgeny Smirnov of Pervy Otdel.

"His imprisonment strikes a blow not only to the judicial system but also to the scientific landscape in Russia."

Golubkin is one of several Russian scientists to be charged with treason in recent years on suspicion of passing sensitive material to foreigners.

Physicist Anatoly Maslov, an expert on hypersonic missiles, was given 14 years in prison last month.