For days, Viktoria Gudyatskaya listened nervously as the escalating fighting along the front lines in eastern Ukraine approached her home in the town of Novoaidar. The thrumming booms of shelling became so insistent that Tuesday Gudyatskaya decided to take her teenage daughter and flee.

"We can hear it now through our closed windows,” she said from the platform at the ramshackle station in Severodonetsk, near her hometown, as she and her daughter prepared to board an early morning westbound train to Kyiv.

For nearly a decade, violence has defined life for the residents of this pocket of eastern Ukraine, where Russian-backed separatists have carved out two enclaves and waged a steady skirmish with Ukrainian soldiers on the other side of the conflict line. But the decision announced by President Vladimir Putin of Russia on Monday night to recognize the two separatist enclaves as independent republics — and to order in Russian troops as "peacemakers” — has suddenly brought new and pressing peril to an already fraught region.