The United Nations (UN) on Tuesday expressed concerns over the UK sending shells made with depleted uranium to Ukraine.

"You have seen the concerns we've expressed over the years about any use of depleted uranium given the consequences of such usage. And those would apply to anyone who provides such armament," Farhan Haq, deputy spokesman for the UN secretary-general, said at a media briefing.

The UN has consistently voiced concerns about the potential consequences of depleted uranium use.

"We have made clear, including through our Office of Disarmament Affairs, concerns about any use of depleted uranium anywhere," Farhan added.

"Depleted uranium is the main by-product of uranium enrichment and is a chemically and radiologically toxic heavy metal," according to the website of the United Nations Environment Programme (UNEP).

"This dense metal is used in munitions for its penetrating ability and as a protective material in armored vehicles," the UNEP said.