A top intelligence official has been moved to a high security jail in Moscow as Vladimir Putin purges his secret services over the botched Ukraine invasion, say reports.
Col-General Sergei Beseda, 68, head of the 5th Service of the Federal Security Service (FSB), was earlier under house arrest.
He has now been placed in pre-trial detention in notorious Lefortovo Prison, suggesting he will face major charges for intelligence failings, it is claimed.
The move will be seen as a warning to other senior Putin aides who are expected to take the blame for the huge Russian death toll in Ukraine.
Beseda's case is being investigated by the Military Investigative Department of the Investigative Committee, said Russian intelligence expert Andrei Soldatov, who revealed the Lefortovo move.
The official who was in charge of FSB intelligence and political subversion in the ex-USSR, had been on a trip to Ukraine shortly before he was detained.
Putin is said to fear that moles leaked invasion plans to the West, and Beseda was detained along with his deputy Anatoly Bolyukh, but had been held under house arrest until now.
The current status of Bolyukh is unclear.
The Russian leader had been convinced by secret services briefings that his troops would be welcomed by many Ukrainians, and achieve a speedy victory.
In reality they have faced implacable opposition.
Lefortovo jail notoriously held political prisoners in the Soviet era and is routinely used to incarcerate suspected traitors.
Last month Putin also fired the deputy head of the Russian national guard.
Beseda had been a longtime trusted Putin secret services official, and was in his role as head of the 5th service of the FSB since 2009.
Russia has not confirmed his arrest or detention in Lefortovo.
Last month The Mirror told how Alexander Bortnikov, director of the Federal Security Service (FSB) and confidant of Putin's, could be the favoured replacement for Vladimir Putin.
Ukrainian intelligence officials claimed a plot to remove the President from the office had allegedly started after Western sanctions crippled the Russian economy.
Sources then claimed Alexander Bortnikov, director of the Federal Security Service (FSB) and confidant of Putin's, could be the favoured replacement.
He was said to be one of the few figures to belong to Putin's powerful inner circle and shares his anti-Western world view, after previously serving alongside the Russian President in the KGB.
But he recently fell out of favour with the Kremlin following Russia's sustained military losses in Ukraine and botched invasion.
He met Putin while they both served as KGB officers in Leningrad in the 70s and plays a key role in ensuring the President maintains power.
Putin left as a lieutenant colonel in 1991, while Bortnikov rose steadily up the ranks.
The pair have been seen hiking previously, and are said to share a love of nature.
