Russia has warned the UK not to provide depleted uranium shells as ammunition for the tanks it is sending to Ukraine, saying they contain a "nuclear component".

Depleted uranium makes weapons more powerful, but it is feared those weapons could be a threat to people in areas where they are used.

Depleted uranium is naturally-occurring uranium, which has been stripped of much - but not all - of its radioactive matter.

It is a waste product from the process through which uranium is enriched for use in nuclear power plants and nuclear weapons.

Uranium is a very dense metal, so depleted uranium can be used to reinforce the armour-plating on tanks.

It can also be put on the tips of bullets, mortar rounds and tank shells, to penetrate conventional tank armour.

Depleted uranium shells sharpen on impact, which further increases their ability to bore through armour, and they ignite after contact.

The UK Ministry of Defence (MoD) says depleted uranium missiles were developed by the US and UK in the 1970s.

They were first used in the Gulf War in 1991, and then in Kosovo in 1999, and during the Iraq War in 2003.

The MoD says it will supply depleted uranium shells to Ukraine's armed forces to use with the 14 Challenger 2 tanks it is sending to Kyiv.

It says the shells will enable Ukrainian tank crews to fire on enemy targets from greater distances, reducing their exposure to counter-fire.

A White House official told the AP news agency that Russia also has stockpiles of depleted uranium weapons, although it is not known if it has used them in Ukraine.

"Depleted uranium shells are not considered to be nuclear weapons," says Dr Marina Miron, from Kings College London.

"They are not meant to poison people. They are used because of their capability to pierce armour."

Depleted uranium is mildly radioactive.

"The fear is that if depleted uranium shells land on the ground, they may contaminate the soil," says Dr Miron. "That is why the US and its Nato allies sparked controversy when they used them in Kosovo."

The UN General Assembly ordered a review into the health effects of depleted uranium weapons in 2007, and international bodies have carried out several further reviews.

The United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) found no significant poisoning was caused by exposure to depleted uranium.

However, the International Atomic Energy Agency (IAEA) says there could be a risk of radiation to individuals who handle fragments of depleted uranium rounds.

A study published in the journal Environmental Pollution in 2019 suggests there may be links between the use of depleted uranium weapons and birth defects in Nasiriyah, in Iraq.

Another concern, says the UN Office for Disarmament Affairs, is that "in a post-conflict environment, the presence of depleted uranium residues can further increase the anxiety of local populations".

A 2022 UN Environment Programme (UNEP) report said it was concerned about possible depleted uranium use in Ukraine, warning it can cause "skin irritation, kidney failure and increase the risks of cancer".

"The chemical toxicity of depleted uranium is considered a more significant issue than the possible impacts of its radioactivity," it says. residues can further increase the anxiety of local populations".

The UK MoD insists that the depleted uranium shells it is sending to Ukraine are not prohibited by any international agreement.

It says that under Article 36 of the First Protocol of 1977 Additional to the Geneva Conventions of 1949, the UK's depleted uranium shells are "capable of being used lawfully in international armed conflict".

President Vladimir Putin has warned that if the UK does send depleted uranium shells to Ukraine, "Russia will have to respond accordingly, given that the West collectively is already beginning to use weapons with a nuclear component".

The MoD replied in a statement: "The British Army has used depleted uranium in its armour-piercing shells for decades. Russia knows this, but is deliberately trying to disinform."

However, Dr Miron says sending depleted uranium shells may backfire on Ukraine and its allies:

"Using them allows Russia to sabre-rattle with its nuclear arsenal, and threaten to use something from it," she says.

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