Many residents have fled the two cities, but hundreds of thousands of people are still living in them, increasingly fearful that they will bear the brunt of a full-blown assault.
The latest Russian troop build-up on the border is not the first time Moscow has concentrated forces there: NATO estimated Russia had as many as 40,000 troops in place earlier in the crisis before Putin pulled them back in June.
But the government’s advance since then may be prompting new action from the Kremlin, after months in which state-controlled Russian media have mounted a sustained campaign of anti-Ukrainian agitation and nationalist pride focused on Crimea.