Russia is treating its own citizens as “bits of meat to fling into the grinder” in Ukraine, Sir Keir Starmer said as he urged Vladimir Putin to end the conflict.
The Prime Minister, speaking at the UN Security Council, said Russia was responsible for “colossal human suffering” as a result of the conflict.
He said Russia, like the UK one of the five permanent members of the Security Council, was behind the “greatest violation of the (UN) charter in a generation”.
“I wonder how Russia can show its face in this building,” he added.
Russia was represented at the UN Security Council by deputy ambassador Dmitry Polyansky, who could be seen studying his mobile phone while the Prime Minister spoke.
The Prime Minister was accompanied at the table by Foreign Secretary David Lammy while his chief of staff Sue Gray was in the audience for his address.
Sir Keir said: “Russia’s invasion of Ukraine is illegal. It threatens global security. And it has caused colossal human suffering.
“Over 35,000 civilians have been killed or injured, six million forced to flee and almost 20,000 Ukrainian children forcefully deported. Kidnapped, to put it bluntly.”
Some 600,000 Russian soldiers had been killed or wounded, Sir Keir said.
“The UN Charter – which they sit here to uphold – speaks of human dignity. Not treating your own citizens as bits of meat to fling into the grinder,” he added.
Sir Keir said “there must be accountability” to show that “aggression cannot pay”.
“Russia started this illegal war. It must end it – and get out of Ukraine,” he said.
Ukraine’s territorial integrity “must be the basis of any just and lasting peace”, he added.
Ahead of his Security Council speech, Sir Keir said Ukraine’s desire to use western missiles to strike targets in Russia will not be the “sole issue” in consideration of Volodymyr Zelensky’s “victory plan” for the war.
The US and UK have so far refused to give Kyiv permission to use the missiles they have supplied against targets in Russia, despite repeated pleas from Mr Zelensky.
The Ukrainian president has said that he is having to fight with his hands tied because he is unable to use the weapons to strike Russian airfields and military facilities which Mr Putin is using to launch deadly air raids, missiles and drones.
In a meeting with Sir Keir in New York, Mr Zelensky said he wanted to “discuss with you some details how to strengthen Ukraine”.
Sir Keir is in New York for the United Nations General Assembly, the annual gathering of world leaders, where Mr Zelensky will present his plan for the next stage of the war to his allies.
In his meeting with Mr Zelensky, the Prime Minister assured him the UK’s support remained “steadfast” and it was an opportunity to “talk through what more needs to be done”.
“These are turning into crucial weeks and months,” Sir Keir added.
Following the meeting, a Downing Street spokeswoman said: “The Prime Minister acknowledged that Ukraine is at a critical point in the war, but he reiterated the UK’s support is ironclad and will continue for as long as it takes.
“President Zelensky set out his ambitions for the coming months and thanked the Prime Minister for the UK’s continued backing.
“They agreed to keep in close contact in the coming weeks.”
Elsewhere, during his remarks to the UN Security Council, Sir Keir also addressed the situation in Sudan as “the worst humanitarian crisis in the world today”.
“The UK has doubled its aid for the victims of this war to almost £100 million. But much more help is needed. The world must step up,” he said.
