Donbas explainer poster
The Donbas region is at the heart of Russia's war on Ukraine. Here's why it's so important
03:52 - Source: CNN
CNN  — 

Phase two of Russia’s invasion of Ukraine – an offensive in the eastern Donbas region – is underway. The question is whether it will be any more successful and competent than phase one, and whether Ukraine will have enough troops and weapons to impede or even block it.

Russian Foreign Minister Sergey Lavrov said Tuesday that the operation in the Donbas is “a very important moment of this entire special operation.”

The Russian goal is clear and publicly stated: to secure all of Ukraine’s eastern regions of Donetsk and Luhansk – parts of which Russian-backed separatists have controlled since 2014. A second aim is to crush the remaining resistance in the port city of Mariupol to consolidate a land bridge linking the Russian region of Rostov with Crimea, which Russia seized from Ukraine eight years ago.

To those ends, Russian forces that were deployed to the north and east of Kyiv have been redeployed and in some cases reconstituted after suffering heavy losses.

Armored personnel carriers of the so-called Donetsk People's Republic drive through a street in Mariupol on April 18.

Now they – and fresher units – are piling into Ukraine from the northeast. US officials estimate that Russia has mobilized some 78 battalion tactical groups in eastern Ukraine – probably about 75,000 troops. Still more are being assembled in Russian border regions.

So far, their tactics have been straight out of the Russian playbook: massive use of artillery, rocket systems and missiles followed by armor advancing. Cities in Luhansk such as Severodonetsk, Popasna and Rubizhne have been reduced to rubble, with power, gas and water supplies destroyed.

But Russian progress on the ground has been modest. That may be a result of not taking time to regroup after the battering they took in February and March.

The Institute for the Study of War (ISW) says that “Russian forces did not take the operational pause that was likely necessary to reconstitute and properly integrate damaged units withdrawn from northeastern Ukraine into operations in eastern Ukraine.”

US officials have assessed that Russia has lost up to 25% of the combat firepower it had before the invasion.

Boxing the Donbas in

CNN analysis of satellite imagery, dozens of social media videos and the statements of both sides suggest the Russians are now trying to advance on three axes.

Imagine the Donbas as a square: Russian forces are already on three sides – leaving only the west open to the Ukrainians for reinforcements and, if necessary, retreat.

From the south and the east, forward Russian units have advanced a few kilometers at best this month. In the south they had already made progress eating into Zaporizhzhia region, which neighbors Donetsk. This week, they began shelling villages well inside Zaporizhzhia.

From the north, after taking the city of Izium at the beginning of this month, they have made little further progress.

What’s unclear at this stage is whether the Russians can and will change gear, and a better-coordinated offensive is around the corner. The report card from the Kyiv campaign suggests otherwise, but US officials believe that for now Russia is still conducting “shaping operations … to make sure they have logistics and sustainment in place.”

Even so, the ISW assesses that “The Russian military is unlikely to have addressed the root causes – poor coordination, the inability to conduct cross-country operations, and low morale – that impeded prior offensives.”

An elderly man walks past an unexploded tail section of a 300mm rocket embedded in the ground in Lysychansk, Luhansk region on April 11.