British ammunition stockpiles are being used for the purpose for which they were intended – degrading Russia's fighting ability, Rishi Sunak has said.
The Prime Minister said he would "not necessarily see it as a negative" that levels of shells and missiles were being run down because they were being used to deter the threat from Vladimir Putin's military.
Mr Sunak's comments came as British-supplied Challenger 2 tanks were poised to begin combat missions in Ukraine.
Appearing before the Liaison Committee of senior MPs, Mr Sunak defended the level of funding allocated to the Ministry of Defence to rebuild stockpiles.
Almost £2bn has been allocated over two years to replenish munitions and strengthen supply chains.
The Prime Minister told the Liaison Committee: "I would not necessarily see it as a negative that our own stockpiles have been drawn down, for the simple fact that if you think about what are those weapons for, they were ultimately there to degrade and deter – primarily – Russian aggression.
"They are being used to do exactly that, they are just being used by the Ukrainians.
"So, in one sense, even though the stockpiles are lower, they are being used for the purpose for which they are intended and degrading the capabilities of an adversary in the process."
Mr Sunak also questioned the credibility of a Chinese peace plan for Ukraine, arguing that China's president Xi Jinping should speak directly to Volodymyr Zelensky.
The Prime Minister also urged Mr Xi to use his influence over Mr Putin to push for an end to the invasion.
"It's clear that Russia is dependent on China," Mr Sunak said, "and we would ask President Xi to use his influence with Putin to urge him to end this war and withdraw from Ukraine as a precondition to any negotiations."
'Fantastic' Challenger 2 tanks arrive in Ukraine
In Ukraine, defence minister Oleksii Reznikov said the "fantastic" Challenger 2 tanks have "recently" arrived in the country.
The UK promised 14 of the vehicles to Ukraine, a move which helped persuade other Western nations to supply their own tanks to aid the fight against the Russian invasion.
Mr Reznikov posted a video on social media showing him taking one of the Challenger 2s "for a spin".
He thanked the Prime Minister and Defence Secretary Ben Wallace, adding: "These fantastic machines will soon begin their combat missions."
Ukrainian tank crews trained in the UK on the vehicles, which are being donated by the Government along with ammunition and spares.
Mr Wallace said the crews "return to their homeland better equipped, but to no less danger".
Russia has condemned the UK's move and predicted the tanks would "burn" on the battlefields of Ukraine.
Mr Putin has also reacted to the UK's decision to supply depleted uranium armour-piercing rounds for the tanks in Ukraine by announcing plans to station tactical nuclear weapons in neighbouring Belarus.