Ukraine is working with the US Federal Bureau of Investigation and American companies to collect evidence of war crimes by Russians, such as geolocation and cellphone information, senior officials have said.

Ukrainian authorities are collecting digital information from battlefields and Ukrainian towns ravaged by the war since Russia invaded the country last February, said Alex Kobzanets, an FBI special agent who previously worked as a legal attaché for the agency in Ukraine.

“Collection of that data, analysis of that data, working through that data is something the FBI has experience working through,” Kobzanets said at the RSA cybersecurity conference in San Francisco.

That work includes looking into cellphone information, forensic analyses of DNA samples, as well as analysis of body parts collected off battlefields, he said.

“The next step is working with national US service providers, and transferring that information… obtaining subscriber information, obtaining geolocation information, where possible,” Kobzanets added.

The work reflects deepening collaboration between the US and Ukraine on the cyber front, where Russia has been a common adversary for both nations. The Russian government did not immediately respond to a request for comment.

The agent added that the US FBI had for the past year and a half been working on helping Ukraine to also identify Russian collaborators and spies operating in Ukraine and the Russian forces that were operating outside of Kiev as the invasion was happening.

US security companies and officials have been a major partner of Ukraine in its efforts to fend off Russian cyberattacks, which it has battled since at least 2015.

Illia Vitiuk, head of the Department of Cyber Information Security in the Security Service of Ukraine, said that while the number of Russian attacks against Ukraine has grown in the last few years, in recent months they have become more targeted.

“It’s very difficult to prove in a criminal case, who is responsible,” said Vitiuk. “It’s very important for us to get as much information about Russian cybercriminals…because we collect all this information and put it into our criminal cases.”

“We do believe that this case about cyber war crimes is something new,” he added. “This is where we have seen the first full scale cyber war.”

• A Reuters report