Russia on Wednesday warned of a "serious" escalation of the Ukraine crisis if Britain gives Kyiv armour piercing ammunition which contains depleted uranium.

"This is a step towards a further escalation, and a serious one at that," Foreign Minister Sergei Lavrov said.

He added that the use of such ammunition would "sharply reduce" Ukraine's ability to "produce high-quality, uncontaminated food".

On Tuesday, President Vladimir Putin said that Moscow would be "forced to react" to any such British moves.

Moscow has been reacting to a written response by a UK defence minister, Annabel Goldie, who was asked whether "any of the ammunition currently being supplied to Ukraine contains depleted uranium".

She responded on Monday by saying that "we will be providing ammunition including armour piercing rounds which contain depleted uranium".

Depleted uranium is a by-product of the nuclear enriching process used to make nuclear fuel or nuclear weapons. It is around 60 percent as radioactive as natural uranium.

Its heaviness lends itself for use in armour piercing rounds as it helps them easily penetrate steel.

The United Nations Environment Program has described it as a "chemically and radiologically toxic heavy metal".