3 scientists behind Putin's 'unstoppable' missiles were jailed on charges of treason. Russian researchers say they are now living in fear.

• Three Russian scientists involved in missile development have been arrested, according to reports.
• The scientists are accused of treason, a charge that carries up to 20 years in prison.

Three scientists involved in the development of Russia's "unstoppable" Kinzhal missiles have been jailed on charges of treason, in a case that has spread alarm among Russian researchers.

In an open letter Monday, members of Institute of Theoretical and Applied Mechanics of the Russian Academy of Sciences' Siberian Branch, which is based in Novosibirsk, said the arrests were having a chilling effect on research.

The cases showed that "any article or report can lead to accusations of high treason", the open letter said.

"In this situation, we are not only afraid for the fate of our colleagues. We just do not understand how to continue to do our job."

They said that that the three scientists — Anatoly Maslov, Alexander Shiplyuk and Valery Zvegintsev — were arrested on false charges.

The scientists had coordinated research to develop Russia's Kinzhal missile systems, Reuters reported.

The weapons, often falsely described as hypersonic, are a type of advanced air-launched ballistic missile capable of carrying over a 1,000 pounds of explosives.

Russia has long described the Kinzhal as an unstoppable hypersonic weapon that it claims is capable of overcoming all known air defense systems.

But Ukraine said it was able to shoot down six of the weapons when they were fired at Kyiv as part of a wave of air attacks on the Ukrainian capital early Tuesday.

The arrest of Shiplyuk, director of the institute's Siberian branch, was reported by Russian state media last August, and Maslov, its chief researcher, last July.

An investigative source told TASS that Maslov was suspected of revealing state secrets on missile technology.

Monday's letter is the first time the arrest of Zvegintsev, who is described as an expert of aerodynamics, has been made public.

In the letter, they say that Zvengintsev was arrested after publishing an article on gas kinetics in an Iranian journal that had been screened before publication to ensure it didn't contain classified information.

According to independent Russian media outlet Meduza, Zvengintsev is being held under house arrest after his detention in April.

Under Russian law, those found guilty of divulging state secrets face up to 20 years in prison.

In the letter, the scientists also referenced the arrest last year of Dmitry Kolker, another researcher at Novosibirsk's Institute of Laser Physics, who had pancreatic cancer at the time of his arrest and died days after being detained.

The colleagues of the men say they were arrested despite the material they are accused of illegally releasing having passed extensive security checks.

"The work we're awarded for and lauded as examples for today becomes grounds for criminal prosecution tomorrow. In these circumstances, it's simply impossible for our institute to work," according to the open letter.

They say younger scientists are being deterred by the arrests from pursuing similar research.

"We think these issues require an urgent solution, otherwise it will be impossible to prevent a catastrophe hanging over domestic aerodynamics," the letter says.