Three Russian academics who have worked on hypersonic missile technology face “very serious accusations”, the Kremlin said on Wednesday, in a treason investigation that has spread alarm through Russia’s scientific community.

Kremlin spokesman Dmitry Peskov said he was aware of an open letter from Siberian scientists in defence of the men, but that the case was a matter for the security services.

In the letter, published on Monday, colleagues of Anatoly Maslov, Alexander Shiplyuk and Valery Zvegintsev protested their innocence and said the prosecutions threatened to inflict grave damage on Russian science.

“We know each of them as a patriot and a decent person who is not capable of doing what the investigating authorities suspect them of,” they said.

President Vladimir Putin has boasted Russia as the global leader in hypersonic missiles, capable of travelling at speeds of up to Mach 10 (12,250 kph) to evade enemy air defences.

On Tuesday, Ukraine said it had managed to destroy six of the weapons in a single night, although Russia disputed this.

Scientists refusing to work in Russia

Notices of academic conferences stretching back over many years show the arrested scientists were frequent participants.

In 2012, Mr Maslov and Mr Shiplyuk presented the results of an experiment on hypersonic missile design at a seminar in Tours, France. 

In 2016, all three were among the authors of a book chapter entitled Hypersonic Short-Duration Facilities for Aerodynamic Research at ITAM, Russia.

The open letter from their colleagues at ITAM — the Khristianovich Institute of Theoretical and Applied Mechanics in Novosibirsk — said the materials the scientists had presented in international forums had been checked repeatedly to ensure they did not include restricted information.

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.”