Scientists have caused alarm by unearthing the bodies of long-dead mammals in an effort to 're-awaken' Stone Age viruses.
The pathogens are believed to have been preserved for millennia in the frozen remains of woolly mammoths and other extinct species in northeast Siberia.
Such prehistoric 'paleoviruses' are unfamiliar to anything inhabiting the Earth today.
The project is being carried out by Russia's State Research Centre of Virology and Biotechnology, known as Vector.
It aims to extract cellular material containing the diseases for lab experiments.
One of the research centre's branches is a former biological weapons facility which, in April 1979 inadvertently released spores of anthrax.
The outbreak killed at least 66 people but Soviet authorities denied the incident ever happened.
In 2004, meanwhile, a researcher accidentally contracted Ebola by pricking herself with a needle containing the virus.
Vector currently hosts 59 maximum security biolabs around the world.
International experts, including Jean-Michel Claverie, are worried about the impact of the new experiments.
The professor of microbiology at the University of Aix-Marseille in France led a team involved in reviving a Siberian 'zombie' virus that had lain frozen under a lake bed for 50,000 years.
However, the professor said his work is focused only on pathogens that could infect single-celled amoeba and not animals or humans.
He described Vector's research as "terrible", reports the Daily Mail.
He said: "I'm totally against it. [It] is very, very risky. Our immune systems have never encountered these type of viruses.
"Some of them could be 200,000 or even 400,000 years old. But ancient viruses that infected animals or humans could still be infectious."
Referring to how secure the research branch itself is, he added: "I would not be very confident that everything is up to date."
But it's not just what Russian scientists might unearth in the Arctic's ancient wastelands.
Permafrost, the huge expanses of frozen ground, are melting due to global warming and could unleash deadly viruses regardless.
Eight years ago there was outbreak of anthrax in reindeer herding community in Russia's far north after a particularly warm summer, killing a 12-year-old boy and seeing at least 72 people hospitalised.
It had come from human and animal remains incased in the thawing permafrost.
The disease had not been seen in the region since 1941.
