A Russian court on Tuesday jailed a 77-year-old scientist for 14 years on treason charges after he was accused of sharing top secret data related to Russia's hypersonic missile programme with Germany.

Several prominent Russian scientists involved with research into hypersonics have been arrested and imprisoned in recent years, accused of sharing state secrets with foreign countries.

A court in Saint Petersburg found physicist Anatoly Maslov "guilty of treason ... and imposed a sentence of 14 years in prison," the press service for the city's courts said in a post on social media.

The case was heard in closed session as it was classified "top secret", the court added.

But Russian media outlets reported that Maslov was accused of passing classified data related to Russia's hypersonic missile programme to German intelligence.

Maslov denied the charges in a court hearing before sentencing last week.

"He said he had done nothing wrong or illegal. He has devoted his life to his family and domestic science ... he did not transfer the alleged information and it doesn't constitute a state secret," the state-run TASS news agency quoted his lawyer as saying.

Maslov, who was arrested in June 2022, specialised in research in hypersonics -- a theoretical field with important applications for Russia's advanced missile programme.

He was the chief researcher at the Institute of Theoretical and Applied Mechanics, part of the Siberian branch of Russia's Academy of Sciences.

At least three other scientists from Novosibirsk -- including the head of the centre where Maslov worked -- have been arrested on different accusations of treason since 2022.

In a video from inside the court on Tuesday, Maslov stood in a glass cage for defendants, wearing a tan jacket, pink shirt and jeans.

His lawyers said the lengthy jail term essentially amounts to a death sentence.

They told the Kommersant daily that he suffered a heart attack in pre-trial detention earlier this year and complained of poor medical care provided to him.

They also said they did not have access to much of the evidence used against him due to it being classified as top secret -- a common approach by Russian prosecutors and judges in cases of treason and espionage.