Boris Johnson and his fellow world leaders will gather for the final day of a G7 summit which has been overshadowed by atrocities in Ukraine.
The leaders issued a joint statement accusing Russian president Vladimir Putin of war crimes after Russian missiles slammed into a shopping centre in Kremenchuk.
The Prime Minister and the leaders of the US, Canada, Japan, France, Germany and Italy condemned the “abominable attack”.
“We stand united with Ukraine in mourning the innocent victims of this brutal attack,” they said.
“Indiscriminate attacks on innocent civilians constitute a war crime.
“Russian President Putin and those responsible will be held to account.”
The strike on Monday came as Ukraine’s president Volodymyr Zelensky appeared via video link at the G7 summit in Germany to call for more sophisticated missile defences.
About 1,000 shoppers were thought to be in the Kremenchuk centre when it was hit.
At least 18 people were dead and more than 60 wounded, but those figures could increase as the debris is searched.
The conflict in Ukraine has dominated the G7 summit in Schloss Elmau, in the Bavarian Alps.
And the battle against the Russian invasion is set to remain at the top of the diplomatic agenda when leaders of Nato, including Mr Johnson, gather in Madrid on Tuesday.
Mr Johnson said the Kremenchuk attack “has shown once again the depths of cruelty and barbarism to which the Russian leader will sink” but it would “strengthen the resolve” of Ukraine and its G7 allies.
The Prime Minister also urged Russian scientists to defect to the UK to escape Mr Putin’s oppression, as he also set out a package of support for Ukrainian researchers.
The Prime Minister said experts who no longer feel safe in Russia should apply to come to a country that “values openness, freedom and the pursuit of knowledge”.
Meanwhile, he announced funding and partnership deals to help Ukrainian academics, whose research has been hit by the Russian invasion, carry on their work in the UK.
At the G7 summit in Germany, Mr Johnson said: “To the Russian scientists and researchers who are looking upon Putin’s violence in dismay, and who no longer feel safe in Russia, you should feel free to apply to come to the UK and work in a country that values openness, freedom and the pursuit of knowledge.”
The plans include a major increase of funding for the “researchers at risk” scheme, putting in a further £9.8 million on top of the initial £3 million, which will see 130 academics come from Ukraine to continue their work.
The UK Government will also provide funding to support the Universities UK International and the Cormack Consultancy Group twinning programme between UK and Ukrainian academic institutions.
The Department for International Trade will step up work under its global entrepreneur programme to offer temporary relocation and mentorship to Ukrainian science and tech business leaders forced out by the invasion.
Mr Johnson said: “People across the UK have opened their hearts and their homes to support those fleeing violence in Ukraine, and our world-leading universities, research institutions and tech businesses are no different.
“Science and technology will be decisive in ensuring Putin fails in Ukraine, and it will be crucial as we rebuild the Ukrainian economy.
“The UK will be with our Ukrainian friends every step of the way.”