The Group of Seven countries said on Friday that volunteer fighters in Ukraine could pose a security threat when they return home.
The group's interior ministers said security problems unleashed by the war also included weapons smuggling, human trafficking, disinformation and threats to key infrastructure.
Having previously grappled with the question of fighters leaving Syria and Iraq, they said they would monitor the return of combatants from Ukraine.
While estimates vary, both Russia and Ukraine have said that thousands of people have volunteered to fight on the Ukrainian side since February.
“Amongst these volunteers, most are motivated by support for Ukraine,” the G7 ministers said in a joint statement after two days of talks in Germany.
“But there are a small number whose battlefield experience could pose a heightened threat upon their return.
“We commit to closely monitoring the possible risks these returning volunteers could pose to our internal security.”
A 14-page statement by Britain, France, Germany, Italy, the US, Canada and Japan said previous armed conflicts had showed that criminals could exploit the war to their advantage.
The ministers said they were “deeply concerned” about the possibility of Ukrainian refugees and displaced people being exploited by criminal networks.
They said they were working closely with Ukraine to prevent firearms, explosives and ammunition in the conflict zone from being traded illegally.
The G7 countries are also closely monitoring the risk of weapons introduced by Russia being diverted, they said.
Crime agency Interpol, which took part in the talks, said illegal weapons were likely to proliferate once the fighting ends.
Ministers were briefed on the use of the agency's iARMS database, which Interpol said had helped in tracing weapons stockpiles diverted by ISIS.
“The Russian war of aggression against Ukraine has shattered the European peace order,” said German Interior Minister Nancy Faeser at a press conference after the talks.
“We, too, have a changed security situation. We have adjusted ourselves to it in the shortest possible time. We will protect our democracies.”
The G7 ministers said the attacks on the Nord Stream gas pipelines showed that key infrastructure needed better protection.
Swedish prosecutors on Friday confirmed findings that the pipelines had been blown up in deliberate acts of sabotage.
Although there is much suspicion over Russian involvement, Moscow denies this and Nato countries have stopped short of directly accusing Russia.
But G7 countries said Russia was behind efforts to manipulate facts and sow distrust, as they set out hybrid threats including disinformation and industrial espionage.
Ms Faeser called on social media companies to strengthen their efforts against disinformation and hate speech.
Japan has said it will make the question of economic security a priority when it takes over the G7 presidency from Germany next year.
