The Group of Seven countries spoke on Thursday about how to keep Ukraine afloat through a perilous winter under Russian bombardment.
At a meeting of G7 foreign ministers, Germany said the group would co-ordinate aid including power generators and cold-weather supplies.
The inevitable cold will be compounded by Russian air strikes that have knocked out an estimated 30 to 40 per cent of Ukraine's power grid.
German Foreign Minister Annalena Baerbock, leading the talks, said Russia was trying to break Ukraine's resistance after suffering setbacks on the battlefield.
“The Russian president, in those places, cities and regions where he can't march in militarily, has chosen a new method of waging war, in which he tries to make people starve, freeze or die of thirst,” she said.
“That is exactly what we as G7 partners will try to prevent with everything we have.”
Germany said it had already provided 100 power generators and was sending beds, blankets, tents and heaters to help Ukrainians endure the winter.
Britain, another G7 member, has separately sent Ukrainian troops back from training exercises with military winter gear.
“We will not accept that the Russian president succeeds in his strategy of breaking Ukraine. We will not accept him hoping for international unity to be broken,” Ms Baerbock said.
“We will not accept that the brutality of this war leads to masses of people, masses of older people, children, young people and families, dying from hunger or cold in the coming months.”
When G7 leaders met in Germany in June, Mr Zelenskyy urged them to put Ukraine in a winning position by December.
But that now seems an unlikely prospect as the two sides dig in for winter, with no peace talks in sight, in the assessment of western officials.
Mr Zelenskyy wants to get his hands on more air defence systems to limit the damage when Russia bombards Ukrainian territory.
A US official said G7 help for Ukraine would cover direct financial support, military aid, humanitarian assistance, reconstruction efforts and initiatives to help refugees.
“There are a number of lines of effort, in particular as we head into winter,” said Howard Solomon, US deputy assistant secretary of state, before the G7 meeting.
As part of their two-day meeting, the G7 foreign ministers were expected to hold talks with African counterparts on Friday.
The meeting comes after Russia threw global food security into fresh doubt by suspending its involvement in a grain deal with Turkey, only to reverse the decision days later.
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Ms Baerbock said the G7 had been caught by surprise at how Russia had sought to turn the tables by blaming western sanctions for food scarcity.
Western powers have stressed that there are no sanctions on Russian agricultural products.
But “while we were passing the sanctions, we didn’t think ahead enough” about how Russia could twist the narrative, Ms Baerbock said at an earlier event with US Secretary of State Antony Blinken.
“We were faced with a situation where suddenly the whole world was speaking about sanctions and that this would also be hitting the prices of food.”
In another response to Russian claims, the International Atomic Energy Agency on Thursday said there was no evidence of “dirty bomb” manufacturing in Ukraine.
Russia had claimed that Ukraine could set off a radioactive weapon to frame Moscow for an escalation, but the IAEA said there was no sign of such activity.