Deputy Chairman of Russia's Security Council Dmitry Medvedev said on Thursday "defeat of a nuclear power in a conventional war may trigger a nuclear war", referring to Russia's military campaign in Ukraine.
In a post on Telegram discussing NATO support for the Ukrainian military, Medvedev said: "Nuclear powers have never lost major conflicts on which their fate depends."
On the same day, Ukraine urged Western allies to hurry up and supply tanks and air defenses to Kyiv, saying it was paying with Ukrainian lives at the front for the slow pace of discussions in foreign capitals.
"We have no time, the world does not have this time," said Andriy Yermak, head of the Ukrainian presidential administration.
(With input from Reuters)