CNN  — 

When Vladimir Putin refocused his war in Ukraine on the country’s east three months ago, he did so bruised by the failures of his initial lunge towards Kyiv and desperate for a face-saving success.

After a slow and bloody march through Luhansk was finalized with the capture of the city of Lysychansk, the Russian President might consider himself halfway there.

But the war has arrived at another crossroads and fighters on both sides are steeling themselves for a third act of fighting that could tip the balance of the conflict.

“It’s a very attritional struggle,” said Justin Bronk, a senior research fellow for Airpower and Technology at the Royal United Services Institute (RUSI), describing the tone of the war after three months of fighting in Donbas.

“It’s a struggle between two armies, both of whom have taken huge losses and are very close to exhaustion.”

Putin’s next move is anticipated to be a drive into Donetsk, which if captured would fulfill the Kremlin’s primary objective: overrunning the entire Donbas region of eastern Ukraine, which has housed Russian-backed separatist factions since 2014.

But when and how that takes place is unclear. While Russia has continued intense airstrikes on various fronts in Ukraine, the US-based think tank Institute for the Study of War (ISW) said Sunday that Russian ground troops were in the middle of an operational pause to “rest, refit, and reconstitute.”

That could give Ukraine’s army time to prepare to defend the parts of Donetsk it still holds; chiefly the industrial belt running south from the city of Sloviansk. And the threat of Ukrainian counter-offensives elsewhere in the country, including the key southern city of Kherson, remains.

The next phase of full-scale fighting, when it does break out, may not be the last. But it may determine the future of Ukraine’s heartland region – and analysts say it will go some considerable way to determining the war’s results.