Ukraine's prosecutor general said on Tuesday that Kyiv suspected a senior Russian air force commander of ordering a missile strike on a children's hospital in central Kyiv in July that killed two people and caused extensive damage.
Shortly after the announcement, Ukraine's SBU security service identified the suspect as Lieutenant General Sergei Kobylash, who it said was the commander of Russia's long-range aviation forces at the time of the attack.
It said in a statement he had since been promoted to head the air force.
In March, the ICC issued an arrest warrant for Kobylash, saying at that time that he was suspected of war crimes including ordering strikes on Ukraine's energy system.
Russia denies carrying out war crimes in Ukraine and says it does not target civilians.
"We are continuing the investigation to find other people responsible for the strike on Okhmatdyt," Kostin told reporters, referring to the hospital.
He stood outside the damaged clinic beside ICC Prosecutor Karim Khan, who is visiting Kyiv.
According to Kostin, the commander ordered the firing of a Kh-101 air-launched cruise missile from a Russian bomber on July 8, the day of the strike.
Khan added that it appeared from various sources that a Kh-101 missile has been identified.
"It does seem from a number of sources and the work that's been done that a missile, a Kh-101 cruise missile, has been identified," Khan said. "A number of factors have to be looked into further."
The ICC has issued arrest warrants for six Russian officials, including President Vladimir Putin.
Putin and Russia's children's ombudsman Maria Lvova-Belova were charged by the court last year with the unlawful deportation of children from occupied parts of Ukraine.
Russia has dismissed ICC war crime arrest warrants as part of a biased Western campaign to discredit Russia.
Russian officials also say such warrants have little real world impact as Moscow is not a member of the court and neither are other major powers, such as the United States and China.
Kostin is leading Ukraine's campaign to prosecute alleged war crimes by Russian forces, and over 140,000 cases are being investigated.
Khan urged actors in the Ukraine war and other conflicts to remain on the side of the law.
"Every leader, every pilot, every soldier - every person has a choice to comply with the law or join this list of infamy of people for whom warrants for crimes against humanity or war crimes have been issued," he said.