Russia's Federal Security Service (FSB) has raided a space research facility after a suspected leak of hypersonic missile secrets to Western spies.
The state space agency Roskosmos said its security staff were co-operating with FSB officers on a criminal case.
Russia's Kommersant daily says about 10 staff at a Roskosmos facility called TsNIIMash are under suspicion. A director's office was searched.
Hypersonic missiles fly at more than five times the speed of sound (Mach 5).
On Thursday the Russia defence ministry released video of two new hypersonic missile systems - called Kinzhal and Avangard. Both can deliver nuclear warheads.
But Russian military expert Pavel Felgenhauer told the BBC he was very sceptical about their effectiveness and dismissed the video as "propaganda". He called the spy investigation "politically embarrassing".
The suspects in the secrets case could be charged with high treason, Kommersant reports.
"It was established that the leak came from TsNIIMash employees," a source close to the FSB investigation told the paper.
"A lot of heads will roll, and for sure this case won't end just with a few dismissals," the source said.
TsNIIMash is a top scientific subsidiary of Roskosmos. It is in the town of Korolyov, in the Moscow region.
Read more on similar topics:
'Propaganda about old projects'
By Russian military analyst Pavel Felgenhauer
These hypersonic missiles are not going to work. They are like the tradition of dragging enormous missiles through Red Square for show.
It's propaganda, and President Putin loves it when the Russian military feeds him that stuff. Guys were working on these projects in Soviet times, but they were put on hold in the 1990s.
Western armed forces also have a need to scare their own parliaments to get more money, so they always exaggerate tenfold the Russian threat.
Kinzhal is just an Iskander [short-range] missile attached to a plane - that creates problems, as it was not designed for such a range. It doesn't have a detachable warhead, and the probability of it disintegrating on re-entry into the atmosphere is much higher. Nor can it hit moving targets. The targeting data has to be put into the missile before launch.
The Avangard gliding warhead is a re-entry vehicle designed to perform erratic hypersonic manoeuvres to baffle defence systems. But that design increases the risk of it disintegrating and it loses accuracy.
These systems add nothing to the Russian nuclear deterrent. The problem is, there is no missile defence to baffle - the systems Mr Putin is talking about do not exist in Western armies.
Pavel Felgenhauer covers military issues for Russia's Novaya Gazeta daily. He spoke to the BBC from Moscow
Russia's defence ministry has broadcast video of what it calls a new generation of nuclear-capable missiles. Some are launched by bombers, others are shown being launched from silos or mobile launch vehicles.
President Vladimir Putin spoke about the systems in March, including the Kinzhal missile, which can reach Mach 10 - about 12,000km/h (7,456mph) - with a range of 2,000km.
The Kinzhal, already in service, is launched from MiG-31 or Tu-22M3 jets. Interfax news agency says Kinzhal-armed MiGs patrol over the Caspian Sea.
The FSB also searched offices at the United Rocket and Space Corporation (ORKK) in Moscow.
Kommersant says a state corporation called Tactical Missile Arms handles hypersonic projects, but TsNIIMash works very closely with it.