Ukraine is collaborating with the Federal Bureau of Investigation and American corporations to gather proof of Russian war crimes, such as geolocation and cellular data, senior authorities said on Tuesday.

Ukrainian authorities have been gathering digital information from war-ravaged battlefields and Ukrainian cities since Russia invaded the nation last February, according to Alex Kobzanets, a former FBI legal attache 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 U.S. service providers, and transferring that information…obtaining subscriber information, obtaining geolocation information, where possible,” Kobzanets added.

The work reflects deepening collaboration between the U.S. 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 U.S. 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.

U.S. 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.”