Oris Johnson and his fellow world leaders will gather for the final day of a G7 summit overshadowed by atrocities in Ukraine.
The leaders issued a joint statement accusing Russian President Vladimir Putin of war crimes after Russian missiles struck a shopping mall in Kremenchuk.
The Prime Minister and the leaders of the USA, Canada, Japan, France, Germany and Italy condemned the “horrific attack”.
“We stand united with Ukraine in mourning over the innocent victims of this brutal attack,” they said.
“Indiscriminate attacks on innocent civilians are a war crime.
“Russian President Putin and those responsible will be held accountable.”
The strike came on Monday when Ukrainian President Volodymyr Zelensky appeared via video link at the G7 summit in Germany asking for more sophisticated missile defense.
About 1,000 buyers were believed to be in the Kremenchuk center when it was hit.
At least 13 people have been killed and more than 40 injured, but those numbers could rise as the rubble is searched.
The conflict in Ukraine dominated the G7 summit in Schloss Elmau, in the Bavarian Alps.
And the fight against the Russian invasion will remain at the top of the diplomatic agenda when NATO leaders, including Mr. Johnson, meeting in Madrid on Tuesday.
Mr Johnson said the Kremenchuk attack “once again showed the depths of cruelty and barbarism to which the Russian leader will sink”, but it will “strengthen the determination” of Ukraine and its G7 allies.
The Prime Minister also urged Russian scientists to move to the UK to escape Mr Putin’s repression, as he also outlined a package of support for Ukrainian researchers.
The prime minister said experts who no longer felt safe in Russia should apply to come to a country that “values openness, freedom and the pursuit of knowledge”.
Meanwhile, he has announced funding and partnership agreements to help Ukrainian academics, whose research has been hit by the Russian invasion, continue their work in the UK.
At the G7 summit in Germany, Mr. Johnson said: “To the Russian scientists and researchers who are watching Putin’s violence with dismay, and who no longer feel safe in Russia, you should feel free to apply to come to the UK and into a country that is open. , appreciate freedom and the pursuit of knowledge. ”
The plans include a major increase in funding for the “Researchers at Risk” scheme, which puts in a further £ 9.8 million over the initial £ 3 million, which will cause 130 academics from Ukraine to continue their work to sit.
The UK Government will also provide funding to support the Universities UK International and the Cormack Consultancy Group twin program between UK and Ukrainian academic institutions.
The Department of International Trade will intensify work under its global entrepreneurship program to provide temporary relocation and mentorship to Ukrainian science and technology business leaders forced 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 institutes and technology enterprises are no different.
“Science and technology will be crucial to ensure Putin’s failure in Ukraine, and it will be crucial if we rebuild the Ukrainian economy.
“The United Kingdom will be every step of the way with our Ukrainian friends.”