The Netherlands has called on governments to increase their financial and political support for the International Criminal Court as it investigates alleged war crimes committed during Russia’s invasion of Ukraine or risk failing to bring those responsible to justice.

Increased backing for the ICC is “critically important,” Dutch foreign minister Wopke Hoekstra said. The court is grappling with an ever-growing list of atrocities committed against civilians in Ukraine, from the targeting of civilians to accusations of rape and murder by Russian soldiers, uncovered after the recapturing of previously occupied towns such as Bucha.

“This is going to be extremely painful, potentially years of hard work and a lot of resources,” he said in an interview. “It is going to take effort, effort and effort. But at the same time there are a million good reasons to do it.”

“It clearly won’t be over in a year. It will take time. But if that is necessary, then let’s accept that and make sure we support it,” he added.

Hoekstra hosted a meeting of EU foreign ministers with the ICC’s chief prosecutor Karim Khan on Monday, where the scale of the court’s task was laid out as it seeks first to collect and collate mounting evidence from Ukraine, and then begin to process it into cases against individuals.

Forty-two countries have referred the war in Ukraine to the ICC, based in the Dutch administrative capital of The Hague, which opened its investigation in early March. Ukraine is not a member of the court but has recognised ICC jurisdiction for events occurring in the country since 2014, when Russia annexed Crimea and fuelled separatist campaigns in the eastern Donbas region.

US president Joe Biden described his Russian counterpart Vladimir Putin last month as a “war criminal”, while other western leaders have said evidence of war crimes committed by his troops is clear. Moscow has accused Kyiv of staging evidence and blamed Ukraine’s soldiers for some atrocities.

Vast amounts of photographic and video footage captured by private citizens as well as evidence collated by professional Ukrainian investigators will need to be sifted by the ICC. Legal experts warn that it will test the limits of a chronically underfunded system that has faced criticism for its failure to bring those responsible for previous war crimes to justice.

“This is a diligent process that will take months and years and the co-operation of many. With successes and setbacks,” admitted Hoekstra. “But for the international community . . . it is of tremendous importance.”

Reports, images and testimonies from towns such as Bucha have “left everyone speechless and all the more committed to bringing to justice those responsible directly and indirectly”, he added.

At Monday’s meeting the Netherlands, Germany and Sweden pledged a combined extra €2.5mn to the ICC, and a number of other countries promised financial and logistical support, Hoekstra said.

But he said far more would be needed to ensure continued support for a legal campaign that would almost certainly be obstructed by Moscow throughout. This was what happened with the court’s probe into the downing of a Malaysia Airlines flight by Russian-backed rebels in eastern Ukraine in 2014 when 298 people were killed.

“Of course, the clear and present challenge now is to provide Ukraine with weapons, make sure there are the most severe sanctions [against Russia], help out with the humanitarian problem and help with the economic problem. That is crystal clear,” Hoekstra said.

“But at the same time we also have to build the second pillar, which is about the long term, which is about justice.”