Russia has accused Ukraine of preparing to manufacture a dirty bomb, a claim Ukraine and the West have rejected.
However, the Western powers are concerned this could be the early stages of a false flag operation for Moscow to launch its own nuclear attack and blame it on Ukraine.
Retired Army Colonel and nuclear weapons expert Hamish De Bretton-Gordon says this is simply Russian scare tactics reflecting weakness on the conventional battlefield, but the West should remain wary of a different form of potential nuclear attack.
"It really is not a realistic way or a weapon"
According to Mr De Bretton-Gordon, "a dirty bomb in its purest form is radiological isotopes such as uranium, plutonium, or even polonium".
"The idea is that you then explode these radiological isotopes or radiological material and that spreads contamination."
A dirty bomb attack has never been successfully implemented anywhere in the world.
The nuclear weapons expert added that "it's always been threatened and it makes a very good storyline in James Bond novels and other terrifying books but, in reality, it is an anathema it really is not a realistic way or a weapon because the likelihood of creating casualties, which is what the Russians want to do, is very low indeed.
"What it does do is have a physiological impact and that's probably the primary aim of Putin and the Russian government at this stage."
Not something "somebody can cook up in their back shed"
A dirty bomb is not the same as an atomic bomb, according to the Centers for Disease Control and Prevention (CDC) – "an atomic bomb, like those bombs, dropped on Hiroshima and Nagasaki, involves the splitting of atoms and a huge release of energy that produces the atomic mushroom cloud".
The dirty bomb "works completely differently and cannot create an atomic blast. Instead, a dirty bomb uses dynamite or other explosives to scatter radioactive dust, smoke, or other material in order to cause radioactive contamination."
Highly refined radioactive material that is used in a nuclear bomb is not required in a dirty bomb – therefore making them cheaper and easier to produce than nuclear weapons.
However, even if the threat of a dirty bomb was credible it is still not a weapon that could be easily deployed.
Mr De Bretton-Gordon said "this is not something a terrorist or somebody can cook up in their back shed and use".
"Getting hold of radiological isotopes is very difficult, highly controlled, and certainly uranium and plutonium would only really be available to states," he said.
"If there is a dirty bomb used with these isotopes, it could only really come from Russia or another nuclear power."
Watch: Ukraine accuses Russia of using phosphorus bombs on steel works plant.
Dangers of a dirty bomb
The main danger from a dirty bomb according to the CDC "is from the explosion, which can cause serious injuries and property damage".
"The radioactive materials used in a dirty bomb would probably not create enough radiation exposure to cause immediate serious illness, except to those people who are very close to the blast site," the CDC said.
However, the radioactive dust and smoke spread farther away could be dangerous to health if it is inhaled."