UNITED NATIONS - UN Secretary-General Antonio Guterres told a Security Council meeting on Ukraine on Thursday that talk of a nuclear conflict is "totally unacceptable" and effectively warned that so-called referendums in areas under Russian control would be annexation.
Referendums on joining Russia are due to take place from Friday to next Tuesday in several largely Russian-held regions in eastern and southern Ukraine, which comprise around 15 per cent of the country's territory.
Mr Guterres told the council ministerial meeting that he was concerned about the plans for "so-called 'referenda'".
Russian Foreign Minister Sergei Lavrov was also set to address the 15-member council on Thursday, but was not in the chamber for Mr Guterres' remarks. "Any annexation of a state's territory by another state resulting from the threat or use of force is a violation of the UN Charter and of international law," Mr Guterres said.
International Criminal Court (ICC) prosecutor Karim Khan told the council that there were "reasonable grounds" to believe crimes within the jurisdiction of the court had been committed in Ukraine.
Mr Khan said the ICC investigation priorities were intentional targeting of civilian objects and the transfer of populations from Ukraine, including children.
The United States has said estimates from a variety of sources, including Moscow, indicate that the authorities have "interrogated, detained, and forcibly deported" up to 1.6 million Ukrainians to Russia since Moscow's invasion.
"The very international order we've gathered here to uphold is being shredded before our eyes. We can't let President Putin get away with it," US Secretary of State Antony Blinken told the council.
Reports from the United Nations rights body show "a catalogue of cruelty - summary executions, sexual violence, torture and other inhumane and degrading treatment against civilians and prisoners of war", said Mr Guterres.
"All these allegations must be thoroughly investigated, to ensure accountability," he said, without directly pointing the finger at Russia.
France, the current head of the Security Council, called the meeting on accountability in Ukraine during the UN General Assembly.
On Wednesday, European Union foreign ministers agreed on the sidelines of the General Assembly to prepare new sanctions on Russia and increase weapon deliveries to Kyiv after Mr Putin ordered the country's first wartime mobilisation since World War II to fight in Ukraine.
Protests have been held across Russia against the move, with over a thousand arrested. Media reports indicated that some of those arrested had been handed draft papers.
Many Russians have sought to travel to other countries to escape being called up to fight as men across the country reported to draft offices.
Germany said on Thursday it is ready under certain circumstances to take in deserters from the Russian army as well as opponents of Mr Putin's regime, according to Interior Minister Nancy Faeser.
"As a rule, deserters threatened by severe repression will receive international protection in Germany," Ms Faeser said in an interview with the Frankfurter Allgemeine Sonntagszeitung.
"Anyone who courageously opposes Putin's regime and therefore puts themselves in great danger can apply for asylum in Germany because of political persecution," she added.