Russian scientists are suspected of making "doomsday weapons" involving deadly Ebola and Marburg virus.
The programme, codenamed Toledo, is thought to be behind the project.
The Moscow FSB spy agency unit is linked to the Salisbury novichock poisonings.
Investigators believe the codename refers to Toledo, Ohio, devastated by a flu bug in 1918 or either the Spanish City, which was hit by a killer plague in 1958.
One ex-UK military intelligence source confirms Russia could be including Ebola and related Marburg virus in its weapons programme, reports The Mirror.
Both highly contagious diseases cause organ failure and internal bleeding and thousands have died from the viruses in Africa.
The UK source told the paper: “Both Russia and the UK have labs studying biological and chemical warfare to learn how to defend against weapons such as novichok.
“But if, simultaneously, Russia is studying how to weaponise Ebola and Marburg, that has horrific possibilities.
“Moscow has repeatedly shown a willingness and capability of using weapons such as novichok, even on the streets of the UK. This steps it up a level.
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“It could mean Russia potentially stepping up research on Ebola and Marburg and looking at its lethality as a weapon.”
Non-profit OpenFacto organisation investigators say they have discovered the Russian Ministry of Defence has a secret unit.
The unit, called the 48th Central Research Institute, is reportedly devoted to studying "rare and lethal" pathogens.
It's also affiliated to the 33rd Central Research Institute, which developed novichok.
OpenFacto states both have been sanctioned for "likely conducting research for the biological weapons" by the US.
It claims the 48th Central Research Institute has been supplying data to FSB unit 68240, the organisation behind Toledo.
Russia expert Bruce Jones said: “Most major powers can develop these hot and very deadly viruses. But they do this defensively.
“At the end of the Cold War, Russia stepped away from any agreements in relation to weaponising them.
“The difference between Russia and the West is that they do have form for using this kind of thing as a weapon, as we saw in the Salisbury novichok attack.”
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