Russia must now be hit with the “maximum level” of sanctions over the atrocities in Ukraine, Foreign Secretary Liz Truss said as she pressured European allies to go further.

The Cabinet minister on Monday called for more weapons of the type Kyiv has called for to be supplied as she criticised Western money flowing into Russian President’s Vladimir Putin’s “war machine”.

Ms Truss hit out at the “butchery” and cited evidence of rape and indiscriminate killing of civilians in Bucha, the Ukrainian town where Moscow’s troops have been pushed back from.

Speaking in Warsaw, Poland, she said she had discussed how the UK can take the “maximum approach” to supplying weapons with her Ukrainian counterpart Dmytro Kuleba.

“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 told a press conference.

“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.”

Ms Truss urged allies to commit to “a tough new wave of sanctions” ahead of meetings of G7 and Nato foreign ministers later this week in Brussels.

“The reality is that money is still flowing from the West into Putin’s war machine – and that has to stop,” Ms Truss said.

She said she would be working with allies to go further banning Russian ships from Western ports, cracking down on Russian banks, going after industries “filling Putin’s war chest, like gold” and to agree “a clear timetable to eliminate our imports of Russian oil, gas and gold”.

Ukrainian President Volodymyr Zelensky has called for fighter jets and tanks to help repel the Russian forces, but the plea has met some resistance from Nato allies hesitant of provoking a wider conflict.

“We also need even more weapons of the type the Ukrainians are asking for,” Ms Truss said, without specifying what arms she supports sending.

“The fact is that being tough is the only approach that will work. 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.”

Speaking beside the Foreign Secretary, Mr Kuleba called for the “most severe” sanctions to be levelled against the Putin regime, including over the Swift banking system.

“Half measures are not enough anymore. I demand from our partners, on behalf of the victims of Bucha and the people of Ukraine, to take the most severe sanctions against Russia this week,” he said.

“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.”

Boris Johnson described the discovery of mass graves in areas where Russian forces had withdrawn from around Kyiv as “sickening” and promised “we will not rest until justice is done”.

“The UK will not stand by whilst this indiscriminate and unforgivable slaughter takes place,” the Prime Minister said.

Ms Truss called for Russia to be suspended from the United Nations’ Human Rights Council and pledged a £10 million civil society fund for Ukraine, including support for organisations dealing with sexual violence.

Mr Johnson, who spoke to Mr Zelensky over the weekend, used a video posted on social media to show his support for the country’s efforts to resist the Russian invasion.

He said: “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 highlighted the Nlaw and Javelin anti-tank systems and Starstreak anti-air missiles which the UK has already supplied to Ukraine, as well as protective helmets and body armour.

But in his talks with Mr Zelensky on Saturday he indicated there will be further help on offer.

Mr Zelensky said there will be a “new package” of “very, very tangible support”, while No 10 said the Prime Minister “committed to continue to step up defensive support”.

No 10 would not be drawn on exactly what could be provided but the Prime Minister’s official spokesman said scenes over the weekend were “barbaric”.