LONDON (REUTERS) - Russia is beefing up its forces for a new assault on Ukraine's eastern Donbas region, setting the stage for a protracted battle that is certain to inflict heavy losses on both sides as the Russians try to encircle Ukraine's fighters, analysts said.
Military analysts are wary of predicting who will win the battle for Ukraine's industrial heartland of Donbas, a crucial conflict that will likely be brutal and ultimately define the course of the war.
"The outcome of the battle could be that both sides will be battered to the point when neither one will be able to conduct an offensive or a counter-offensive," said Mr Konrad Muzyka, director of the Poland-based Rochan consultancy.
"Ukrainians will defend their land to the last man. The Russians will incur significant losses."
An uneasy "frozen" conflict could emerge and last for months with the constant threat of a fresh assault by Moscow, he said.
Russia describes its campaign, which began in February, as a special operation to degrade Ukraine's military capabilities and root out dangerous nationalists.
A protracted battle would frustrate any hopes that President Vladimir Putin has of declaring a significant victory in time for May 9 when Russia marks victory over Nazi Germany in World War II with a huge military parade that the Kremlin leader oversees every year.
Outgunned by Russia, Ukrainian President Volodymyr Zelenksy has called on the West to help save his country. He wants Nato to help police its airspace and the West to ship more fighter aircraft, missiles and anti-tank rockets.
Moscow began pulling out its forces from near Kyiv and Ukraine's north late last month in order, it said, to focus on taking the Donbas.
Even without reinforcements now arriving, Russia's invasion has slowly pushed back Ukrainian fighters in some areas of the Donbas and secured around 90 per cent of Luhansk region, said Mr Nick Reynolds, a land warfare analyst at the Rusi think-tank in London.
Ukraine's troops have held on more robustly in Donetsk, which together with Luhansk makes up Russian-speaking Donbas, a swathe of which was seized by Russia-backed separatists in 2014.
A significant Ukrainian contingent has been dug in since then.
Moscow could try to punch through Ukraine's eastern front while advancing with troops, tanks and armoured vehicles from the north and south in a pincer movement. That would seek to outflank and surround Ukrainian forces from behind, the analysts said.
Ukraine will likely try to avoid open tank battles, using artillery to target supply lines and equipment, and send raiding teams to attack convoys and logistics lines, analysts said.
Fearing that their forces could be encircled, Ukrainian strategists will have to evaluate constantly whether they should pull the fighters back to avoid a quick, chaotic retreat in which they could become separated or smashed by artillery and aerial fire.
"It's disengaging from ... the front line that's going to be the problem. That's one of the calls the Ukrainians are going to have to make," Mr Reynolds said.
Can Mariupol holdout?
At the southern edge of Donetsk region on the Sea of Azov, Russia looks poised to wrest full control of the besieged port city of Mariupol where exhausted Ukrainian marines have been desperately holding out, Mr Reynolds said.
"Unless the Russian advance runs out of steam with logistics and morale, I think Mariupol is unfortunately done... If Mariupol falls, it frees up a lot of manpower for other parts of (Russia's) advance," Mr Reynolds said.
Russia could launch its fresh Donbas assault as early as the end of this week or next week when reinforcements have arrived from Russia and Belarus as well as Kyiv, Chernihiv and Sumy in Ukraine, Mr Muzyka said.
US private firm Maxar released satellite images taken on Friday showing an eight-mile-long Russian military convoy of armoured vehicles and trucks towing artillery and support kit east of the Ukrainian city of Kharkiv heading south towards the Donbas.
Russia's northern pincer advance would likely push south from the town of Izyum that lies strategically on the road towards the Ukrainian-held towns of Sloviansk and Kramatorsk.
The governor of Donetsk region said on Tuesday (April 12) that Russia looked like it was in the final phase of regrouping and was pounding the region with shelling around the clock.
"We are going to see a prolonged battle for Donbas. Russia has chances to prevail but only because of its preponderance of firepower and equipment and manpower, and not because of operational superiority," said Mr Muzyka.