Germany's former chancellor Angela Merkel warned that taking Vladimir Putin's words seriously is "a sign of political wisdom" not weakness.
Merkel, who left office two months before the Ukraine war began, was speaking about an answer she had given in June about Putin's character.
"I replied that one should take his words seriously," said Merkel, while speaking at the inauguration of the Helmut Kohl Foundation.
"And today, in view of the developments of the last few days, I would like to add: taking words seriously, not dismissing them out of hand as just a bluff, but dealing with them seriously is by no means a sign of weakness or appeasement, but a sign of political wisdom."
She added that this wisdom would help to "preserve room for manoeuvre, or at least as importantly, even to develop new ones".
Her comments come after Putin recently made a thinly veiled threat to use Russia's nuclear arsenal.
The Russian president warned the West that Moscow "has various means of destruction...more modern than those of NATO countries".
He said that "when the territorial integrity of our country is threatened, to protect Russia and our people, we will certainly use all the means at our disposal."
"It's not a bluff," he added.
It comes as a successful Kyiv counteroffensive has sparked an escalation in the war. Russian-occupied areas in the east and south have held "referendums" on joining Russia, which the West has decried as fake. Putin is expected to annex four regions on Friday.