Police in London have received about 50 referrals of possible war crimes linked to Ukraine since the Russian invasion was launched two months ago.
The Metropolitan Police is collecting evidence for the International Criminal Court’s investigation.
Much of the information from people in Britain passed to the Met's war crimes team — part of the force’s counter terrorism command — relates to attack on civilians.
Most reports being analysed by detectives and specialist officers relate to incidents since Russia's invasion began on February 24.
Evidence may then be shared with the ICC for its probe announced on March 2.
The force is appealing for anyone in the UK who has direct evidence of potential war crimes to come forward.
This relates to any incidents of possible war crimes in Ukraine from November 2013 to present.
Detective Chief Superintendent Dominic Murphy, head of operations for the Met’s counter terrorism command, urged families hosting refugees from Ukraine to contact the force if their guests have witnessed or been the victims of possible war crimes.
“Since the start of the recent military activity in February, our officers have been proactively engaging with Ukrainian communities in the UK,” he said.
“This is to make sure anyone here in the UK who has received direct evidence of potential war crimes knows that this can be reported to us, but also to make sure that anyone affected by these terrible events can also be given the support and help that they might need.
“We’ve had around 50 referrals into us and we expect that number to grow over the coming weeks as more and more people who fled from Ukraine arrive here in the UK.
“We want to make sure those people know we’re here and that we’re ready to receive any evidence of war crimes from them, as well as provide them with the support and help that they might need in relation to that.
“I’d also ask any households across the country who have volunteered to host Ukrainian people that should you come into contact with anyone who might have been witness to or victim of possible war crimes, then you encourage them to contact us. Please let them know we are here and that we can help them.”
Anyone with direct evidence of possible war crimes in Ukraine can report them via the Met's online reporting portal.
The appeal comes as the UN on Friday accused Russia of taking action in Ukraine “that may amount to war crimes”, including indiscriminate bombing that killed civilians and destroyed schools and hospitals.
“Russian armed forces have indiscriminately shelled and bombed populated areas, killing civilians and wrecking hospitals, schools and other civilian infrastructure, actions that may amount to war crimes,” said Ravina Shamdasani, spokeswoman for the UN's Office of the High Commissioner for Human Rights.
US President Joe Biden has called for Russian President Vladimir Putin to be tried for war crimes over civilian deaths in Ukraine.
After images emerged in early April showing bodies buried in a mass grave and civilians shot with their hands behind their backs in the Ukrainian town of Bucha, western leaders condemned the Russian military.
The discoveries were made after invading troops withdrew from the commuter town north-west of Kyiv.
“You may remember I got criticised for calling Putin a war criminal,” Mr Biden said.
“Well, the truth of the matter — we saw it happen in Bucha — he is a war criminal.”