After more than four months of ferocious fighting, Russia claimed a key victory: full 

 control over one of the two provinces in Ukraine’s eastern industrial heartland.

But Moscow’s seizure of the last major stronghold of Ukrainian resistance in Luhansk province came at a steep price. The critical question now is whether Russia can muster enough strength for a new offensive to complete its capture of the Donbas and make gains elsewhere in Ukraine.

“Yes, the Russians have seized the Luhansk region, but at what price?” asked Oleh Zhdanov, a military analyst in Ukraine, noting that some Russian units involved in the battle lost up to a half their soldiers.

Even President Vladimir Putin acknowledged Monday that Russian troops involved in action in Luhansk need to “take some rest and beef up their combat capability.”

That raises doubts about whether Moscow’s forces and their separatist allies are ready to quickly thrust deeper into Donetsk, the other province that makes up the Donbas. Observers estimated in recent weeks that Russia controlled about half of Donetsk, and battle lines have changed little since then.

What happens in the Donbas could determine the course of the war. If Russia succeeds there, it could free up its forces to grab even more land and dictate the terms of any peace agreement. If Ukraine, on the other hand, manages to pin the Russians down for a protracted period, it could build up the resources for a counteroffensive.