The European Union must take seriously the possibility of Russia using nuclear weapons. Josep Borrell, head of EU diplomacy, told the British broadcaster BBC on Saturday.
"Certainly it's a dangerous moment because the Russian army has been pushed into a corner, and Putin's reaction - threatening using nuclear arms - it's very bad," Mr Borrell said.
Borrell expressed the opinion that European countries should continue to support Ukraine, including with weapons, and not stop the policy of anti-Russian sanctions.
"Otherwise, we can finish the war, but we will not have peace, and we will have another war," he said.
In a rare address to the nation earlier this week, Mr Putin said his country had "various weapons of destruction" and would "use all the means available to us", adding: "I'm not bluffing."
"When people say it is not a bluff, you have to take them seriously," Mr Borrell said.