President Vladimir Putin has said that Russia would be "forced to react", said, if the UK were to send depleted uranium shells to Ukraine.
He said that the West was using "nuclear component" weapons.
In addition to Challenger 2 tanks, the UK announced it would give Kyiv armour-piercing bullets, but stated there was little radiation present.
The Ministry of Defence (MoD) says depleted uranium "is a standard component and has nothing to do with nuclear weapons".
What are depleted uranium shells?
Public Health says depleted uranium is a dense metal produced as a by-product of enrichment of natural uranium for nuclear fuel.
These munitions were used in both Gulf Wars and in Serbia and Kosovo.
When a weapon made with a depleted uranium tip or core strikes a solid object, such as the side of a tank, it goes straight through it and then erupts in a burning cloud of vapour.
Its use has sparked worries about potential health risks from exposure to the uranium being dispersed.
Several studies have claimed that there is no indication of risk, although their findings are still debatable. In 2008, the European Parliament requested further information on the origins of depleted uranium and its scientific basis.
Is depleted uranium radioactive?
It is still radioactive, but at a much lower level than the starting material. It is used in armour-piercing shells and bombs, to give them more penetrating power.
Due to quick tissue damage, radiation can result in radiation sickness. Such harm is seen after radiation, workplace mishaps, and nuclear weapon use.
The cells that reproduce quickly, such as those in the skin, bone marrow, and gut lining, are most affected. Extreme exposure quickly results in death and damages tissue.
Genetic mutations brought on by radiation can potentially raise the risk of developing cancer. Often, it is expected that the danger would rise when the dose is increased without a set minimum.
