Ms. Merkel’s speech followed a meeting of the Group of 20 leaders in Brisbane, Australia, where the souring relations were on full display as Western leaders pressed Mr. Putin on Russia’s Crimea policy and support for Ukrainian separatists — and the Russian leader slipped out early, insisting he had business to attend to back home.

President Obama said his meeting with Russia’s leader at the summit meeting was “businesslike and blunt.” Prime Minister David Cameron of Britain, who in the days leading up to Brisbane had likened Mr. Putin’s actions to those of Nazi Germany, told the Russian president that he was at a fork in the road over Ukraine. Prime Minister Stephen Harper of Canada told Mr. Putin, “Well, I guess I’ll shake your hand, but I have only one thing to say to you: ‘You need to get out of Ukraine.’ ”

As the meeting wound up, Russia expelled multiple diplomats after Germany, Poland and Lithuania apparently took similar actions against Russian envoys accused of spying. Sweden, which for days recently was transfixed by the appearance off its coast of what appeared to be a Russian submarine, has also said Russia increased its spying this year.

But the real surprise was the tone taken by Ms. Merkel in her speech after the summit meeting. In recent weeks, the chancellor has made it clear she sees that “Putin is testing us,” as she told parliamentary deputies. In a discussion at the university, she developed that thought further, asking whether Mr. Putin’s annexation of Crimea and military and political interference in eastern Ukraine meant a return to the times when Moscow decided the fate of its near neighbors.

Ms. Merkel seemed to acknowledge that the West should consider Russian sensitivities to Ukraine — with long, close ties to Russia — joining NATO. But she said that was not the case with Ukraine drawing closer to the European Union, which sparked the long-running unrest and conflict with Russia.