Dmitry Medvedev, a long-time ally of Russian President Vladimir Putin, has laid out the country's new deterrence policy against Western "aggression," and warned that provocations by Ukraine and its allies could result in nuclear war.

Volodymyr Zelenskiy said any sign of weakness from his Western allies may embolden Russian President Vladimir Putin as he kicked off a three-day tour of European countries to rally support for his plan to end the war.

Russia has sustained more than 600,000 casualties during the war in Ukraine, a sign of losses accelerating out of proportion with its gains, Pentagon officials said. Since the summer, Moscow has continued to take territory in Ukraine's eastern region of Donetsk,