Ukrainian President Volodymyr Zelenskiy told the international conference that Russian missiles had struck two community centres in the west of Ukraine, killing 20 people, including three children, and wounding many more.
Russia has repeatedly denied involvement in war crimes and deliberately targeting civilians since it invaded Ukraine in February.
It says it launched a "special military operation" to protect Russian speakers and root out dangerous nationalists.
Ukraine says Russia is waging an unprovoked war of conquest.
On Thursday, 45 countries at the conference in The Hague - headquarters of the International Criminal Court (ICC) - signed a political declaration to work together on investigations into war crimes in Ukraine.
Those countries included European Union members as well as the United Kingdom, the United States, Canada, Mexico and Australia.
Steps they will take include creating an umbrella group to avoid duplicating investigations, training Ukrainian prosecutors and expanding the number of forensic teams operating in Ukraine.
They also pledged 20 million euros ($A30 million) to assist the ICC as well as the prosecutor general's office in Ukraine and United Nations support efforts.
With 23,000 war crimes investigations now open and different countries heading teams, evidence needs to be credible and organised, officials said.
Dutch Foreign Minister Wopke Hoekstra said governments were galvanised by images of "innocent civilians being butchered with their hands tied behind their back, women and men being raped and sometimes family members being forced to look at that".
Separately, Hoekstra said the Netherlands would consider setting up an international Ukraine war crimes tribunal, in part because neither Ukraine nor Russia are members of the ICC.
"We have to fill a vacuum and the ICC here doesn't have the jurisdictions so I can imagine we do look into coming up with such a tribunal... We will take a look into this," he said.
Since invading in February, Russian forces have bombed Ukrainian cities to ruins and left behind bodies in the streets of towns and villages they occupied.
Ukraine says tens of thousands of civilians have died.
Russia denies responsibility.
There have also been some reports of Ukrainians mistreating Russian prisoners although the vast majority of accusations documented by bodies such as the UN are of alleged atrocities committed by Russian invaders and their proxies.
"As this meeting takes place, Russian forces continue to commit atrocities in Ukraine with harrowing intensity," said US envoy Uzra Zeya, who attended the meeting.
"With each day the war crimes mount: rape, torture, extrajudicial executions, disappearances, forced deportations, attacks on schools, hospitals, playgrounds, apartment buildings, grain silos, water and gas facilities."
The European Union's justice commissioner, Didier Reynders, noted that war crimes and genocide suspects were still at large from conflicts dating back decades in places such as Rwanda, Darfur, Syria, Congo and the Balkans.
ICC chief Prosecutor Karim Khan said there were reasons for hope because more than 40 countries were now seeking action on Ukraine through the court.
The ICC has sent the largest field team in its 20-year history to investigate in Ukraine.
"At a time like this, the law cannot be a spectator. The law cannot recline in comfort in The Hague," he said.
