Gabriel - at an event commemorating World War I with French Prime Minister Manuel Valls - warned of resurgent nationalist forces both within Europe and "in its neighbourhood".
He said that good news several months ago from Ukraine - including an end to bloody violence against protesters - had since given way to "an ongoing military confrontation" and the realization that "Russia is apparently willing to let tanks cross European borders."
"Suddenly, we are being dragged from the observer's position into a long smouldering and incendiary conflict, which is also demanding a price from Europe in the form of sanctions against Russia," he said.
Foreign minister Frank-Walter Steinmeier, meanwhile, called the danger of Europe splitting a “real one”.
Responsible foreign policy has to make sure that this is prevented,” he told Swiss newspaper the Neue Zürcher Zeitung.