The minister said that Storm Shadows missiles will be provided to Ukraine's military.

Sky News understands that some of the missiles are already in Ukraine - with Mr Wallace saying the projectiles "are now going into or are in the country itself."

Ukraine has long been calling for such weapons, but the US and other countries have been unwilling to supply them in case strikes inside Russia lead to escalation.

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Storm Shadow is a long-range, air-launched cruise missile developed by British Aerospace and a French company, which carries a 450kg conventional warhead to a range of up to 200 miles (300km).

Speaking in the House of Commons, Mr Wallace said: "The donation of these weapons systems gives Ukraine the best chance to defend themselves against Russia's continued brutality, especially the deliberate targeting of Ukrainian civilian infrastructure, which is against international law.

"Ukraine has a right to be able to defend itself against this."

He added that the missiles would be for use "within Ukrainian sovereign territory".

Missiles being launched into Russia would raise the likelihood of a greater Russian reaction.

In response to reports the deal had been done, Moscow said the move would require an "adequate response from our military".

Mr Wallace said he would not give in-depth details of the capabilities of Storm Shadow - but said: "These weapons will give Ukraine new capability, members should recognise that these systems are not even in the same league as the Russian AS-24 killjoy hypersonic missile," or "even the Kalibr cruise missile with a range of over 2,000 kilometres, roughly seven times that of a Storm Shadow missile".

In his speech, the defence secretary laid out some of the ways Russia had been attacking Ukraine - including allegations it had used white phosphorous.

He said that using such weapons - "which burn at 800C" - is in contravention of "protocol three of the Convention of Certain Conventional Weapons".