The owner of a war-zone mobile hospital in eastern Ukraine has instructed his doctors to “castrate captured Russian soldiers”.
It comes as Ukraine said it would not accept ultimatums from Russia after Moscow demanded it stop defending besieged Mariupol.
Hundreds of thousands of civilians are suffering through Russian bombardments laying waste to the port city.
Gennadiy Druzenko, 49, told Ukraine-24 channel about Russian military prisoners of war: “I have always been a great humanist and said that if a man is wounded, he is no longer an enemy but a patient.
“But now [I gave] very strict orders to castrate all [captured Russian] men, because they are cockroaches, not people.”
Since 2014, some 500 doctors - male and female - have worked with Druzenko’s mobile hospital.
A lawyer by training, he set up the First Voluntary Mobile Hospital which deploys civilian doctors and nurses in the conflict zone close to the separatist republics in eastern Ukraine.
He also told famous Russian TV host Yevgeny Kiselyov on Ukraine-24 channel: “Believe all doctors who saved the patients - Russians will die here.
“Die in large numbers.
“Those who [come here] will remember their nightmare on Ukrainian soil.
“Like the Germans remember Stalingrad.”
The Russian Investigative Committee opened a criminal case into the comments, which means that if Druzenko is captured he will face trial under Russian law.
The head of the committee Alexander Bastrykin, a former university classmate of Vladimir Putin, initiated a criminal case over his castration demand which is “contrary to the law and the norms of medical ethics”.
He said: "The head of the Ukrainian Mobile Hospital project, Gennady Druzenko, called for violence against captured soldiers of the Russian Armed Forces live on a Ukrainian TV channel.
"He gave this instruction to the doctors of mobile hospitals.”
Druzenko is set to be put on Russia ’s international wanted list.
Mariupol has become a focal point of Russia's assault on Ukraine, but attacks were also reported to have intensified on the country's second city Kharkiv on Monday.
The conflict has driven almost a quarter of Ukraine's 44 million people from their homes, and Germany predicted the refugee number could reach as high as 10million in coming
weeks.
Europe said Russia was using refugees as a tool and that it was prepared to take more action on top of existing sanctions to isolate Russia from global finances and trade.
Russia's military had ordered residents of Mariupol to surrender by 5am local time on Monday, saying those who did so could leave, while those who stayed would be handed to tribunals run by Moscow-backed separatists.
President Volodymyr Zelensky's Government responded that it would never bow to ultimatums and said cities such as the capital Kyiv, Mariupol and Kharkiv would always defy occupation.
"There can be no question of any surrender" in Mariupol said Ukrainian Deputy Prime Minister Iryna Vereshchuk.
Russia's invasion, now in its fourth week, has largely stalled, failing to capture any major city, but causing massive destruction to residential areas.
