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Ukrainian Foreign Minister Dmytro Kuleba has called for the “most severe” sanctions to be imposed on Russia after a meeting with UK Foreign Secretary Liz Truss in Poland.
Russian forces have been accused of atrocities in the Ukrainian town of Bucha, where a mass grave was discovered.
“It is time to put all hesitation, reluctance, business-wise arguments aside and think about human suffering and the need to stop the Russian war machine until it kills and destroys more on its way.”
On Monday, she said more weapons of the type Kyiv has called for should be supplied to Ukraine.
She was also critical that western money has been flowing into Russian President’s Vladimir Putin’s war effort.
Ms Truss said there was evidence of rape and the indiscriminate killing of civilians in Bucha during Russia's occupation of the town.
Speaking in Warsaw, she said she spoke to Mr Kuleba about how the UK could take the “maximum approach” to supplying weapons to Ukraine.
“The idea that we should wait for something else bad to happen is just completely wrong. The worst has already happened, we’ve already seen appalling atrocities committed in Ukraine with complete impunity,” she said.
“That is why we want to go to the maximum level of sanctions with our allies and partners and that is why we are pulling the stops out in terms of supplying Ukraine with the support they need to end this appalling war.”
“The reality is that money is still flowing from the West into Putin’s war machine – and that has to stop,” she said.
She will work with allies to ban Russian ships from western ports and crack down on Russian banks, she said.
She said she planned to go after industries “filling Putin’s war chest, like gold” and to agree to “a clear timetable to eliminate our imports of Russian oil, gas and gold”.
Ukrainian President Volodymyr Zelenskyy has called for fighter jets and tanks to help repel Russian forces, but the plea has met some resistance from Nato allies wary of provoking a wider conflict.
“The fact is that being tough is the only approach that will work,” Ms Truss said.
"Putin has escalated this war and this approach is vital to ensuring he loses in Ukraine and that we see a full withdrawal of Russian troops and Ukraine’s hand is strengthened at the negotiating table.”
She has called for Russia to be suspended from the UN Human Rights Council and pledged a £10 million ($13m) civil society fund for Ukraine, including support for organisations dealing with sexual violence.
Also on Monday, UK Prime Minister Boris Johnson described the discovery of mass graves in areas around Kyiv once occupied by Russian forces as “sickening” and promised that “we will not rest until justice is done”.
“The UK will not stand by while this indiscriminate and unforgivable slaughter takes place,” he said.
Mr Johnson, who spoke to Mr Zelenskyy at the weekend, used a video posted on social media to show his support for the country’s efforts to resist the invasion.
“All the tanks and guns in Vladimir Putin’s arsenal will never break the spirit of Ukraine’s people or conquer their homeland,” Mr Johnson said.
He highlighted the Nlaw and Javelin anti-tank systems and Starstreak anti-air missiles that the UK has supplied to Ukraine, as well as helmets and body armour.
But in his talks with Mr Zelenskyy on Saturday, Mr Johnson indicated that the UK would offer further help.
Mr Zelenskyy said there would be a package of “very, very tangible support”, while the UK said Mr Johnson “committed to continue to step up defensive support”.
The UK would not be drawn on exactly what would be provided.