Russia Ukraine war: Next part of Vladimir Putin's plan after declaring victory in Mariupol

Speculation is rife over the next phase of Vladimir Putin's plan after claiming victory in the besieged city of Mariupol, with experts warning the Russian leader's next move will likely be a brutal one.

On Thursday, the Russian leader claimed the "liberation" of Mariupol, after nearly two months of relentless attacks on the key port city.

"The completion of combat work to liberate Mariupol is a success," Putin said alongside Defence Minister Sergei Shoigu.

Around 2000 Ukrainians are still inside the Azovstal steelworks site, where they have been defending against the advancing Russian forces.

Researchers from the Institute for the Study of War (ISW) said the next phase of Putin's plan will see his forces starving out the remaining Ukrainian defenders.

"Russian forces will attempt to starve out remaining Ukrainian defenders in the Azovstal steel plant rather than clear it through likely costly assaults," an assessment from the ISW stated.

A soldier of the Azov battalion walks inside the regional administration building that was heavily damaged after a Russian attack last month, in Kharkiv, Ukraine, Thursday, April 21, 2022. Photo / AP

"The Kremlin will spin the (still incomplete) capture of Mariupol into a major victory in Ukraine to compensate for stalled or failed Russian offensives elsewhere."

In the televised meeting, Putin ordered Shoigu to call off a planned storming of the plant, instead telling the military to seal off the steelworks site "so that not even a fly" can get through.

"There is no need to climb into these catacombs and crawl underground through these industrial facilities. Block off this industrial area so that not even a fly can escape," the Russian leader said.

Ukraine has appealed for an immediate humanitarian corridor to allow civilians and wounded fighters to be evacuated from the Azovstal steel plant.

"They have almost no food, water, essential medicine," Ukraine's foreign ministry said.

The ISW assessment suggested the slowing down of operations in Mariupol is likely to allow for "significant combat power" to be deployed to other offensive operations in the coming days and weeks.

"ISW has consistently assessed that Russian battalion tactical groups (BTGs) have taken high casualties in the battle of Mariupol, are degraded, and are unlikely to possess their full complement of personnel (800-900 at full strength)," the report states.

"Russian forces will certainly be able to redeploy some units from Mariupol to offensive operations elsewhere – but Ukrainian forces have succeeded in tying down and degrading a substantial Russian force, and the Kremlin's declaration of victory has not inherently freed up 12 BTGs worth of combat power for other operations."

Some portion of the Russian forces will need to stay in Mariupol to maintain the siege on the Azovstal plant and secure the rest of the city against any remaining pockets of Ukrainian defenders.

The fate of Mariupol has become crucial to Russia, after Putin was forced to change his original plans.

Capturing the city would help the Russian leader create a land bridge covering territories already under its control, including Crimea, which would deprive Ukraine of its industrial heartland and most of its coastline.

Late on Monday night, Russian forces launched a major offensive into eastern Ukraine, with the assault coming weeks after Putin was forced to pull his forces out of northern parts of Ukraine after they repeatedly failed to capture the capital of Kyiv.

It was an embarrassing retreat for the Russian leader, who had been confident his military would overwhelm Ukrainian forces shortly after the invasion began on February 24.

Olexiy Arestovych, an adviser to Ukraine's President Volodymyr Zelensky, said Russia had since diverted forces to fight for all of Lugansk and Donetsk, two regions of Ukraine controlled by pro-Moscow separatists.

"They won't succeed," Arestovych warned.

Women choose second hand clothes donated by local volunteers in Chernihiv, Ukraine, on Thursday, April 21, 2022. Photo / AP

President Joe Biden said Putin was doomed to failure, announcing $US800 million ($1.197 billion) in extra US military aid including howitzers and tactical drones.

"Our unity at home with our allies and partners, and our unity with the Ukrainian people, is sending an unmistakable message to Putin – he will never succeed in dominating and occupying all of Ukraine," he said.

This comes amid speculation from the ISW that Putin will find it difficult to win the "battle for Donbas".

"The Russian offensive in the east is unlikely to be dramatically more successful than previous Russian offensives, but Russian forces may be able to wear down Ukrainian defenders or achieve limited gains," the institute stated.

ISW's new assessment claimed Russian forces may have not taken the "operational pause" necessary to properly reinstate previously damaged units and prepare them for this new offensive.

"As we have assessed previously, Russian forces withdrawn from around Kyiv and going back to fight in Donbas have, at best, been patched up and filled out with soldiers from other damaged units, and the Russian military has few, if any, cohesive units not previously deployed to Ukraine to funnel into new operations," the institute noted.

"Frequent reports of disastrously low Russian morale and continuing logistics challenges indicate the effective combat power of Russian units in eastern Ukraine is a fraction of their on-paper strength in numbers of battalion tactical groups."

ISW researchers did concede that Russian forces may be able to wear down Ukrainian forces in the east with a "heavy concentration of firepower and sheer weight of numbers".

However, this would still likely come at a "high cost".

"A sudden and dramatic Russian offensive success remains highly unlikely, however, and Ukrainian tactical losses would not spell the end of the campaign in eastern Ukraine, much less the war as a whole," the assessment stated.