The Azovstal steel and iron works is the last stand for Ukrainian troops inside the besieged city of Mariupol, which is now almost entirely occupied by Russian forces.
Hundreds of civilians are thought to be holed up in bomb shelters beneath the industrial complex alongside soldiers, marines and medics.
Initially, the site was expected to be the scene of a bloody battle, with Russian units attempting to seek out the remaining Ukrainian forces in the tunnels below.
Putin switches strategy
But on Thursday, President Vladimir Putin changed his strategy, calling off the Russian assault and ordering a blockade of the complex instead.
Information about the situation on the ground is thin. Most of the reports come from Russian military units, who have a vested interest in appearing to have control of the site.
So what has happened at Azovstal so far and how has this industrial facility become the final outpost in the long and brutal battle for Mariupol?
As Russian forces made territorial gains in other parts of Mariupol, the Azovstal plant remained in Ukrainian hands.
The leader of the so-called Donetsk People’s Republic (DPR) claimed the site was one of the main hubs of resistance to Russian forces inside Mariupol on 30 March.
Three days later, a post on Chechen leader Ramzan Kadryov’s Telegram channel said that his forces had begun an assault on the facility.
Chechen forces launch assault
Chechen forces have been based in an area near the eastern edge of the Azovstal plant for some weeks, according to Janes, a global intelligence company.
“It seems in the east, in the shallow suburb between the [Azovstal] plant and the countryside, the Chechens and whoever else was fighting there had a bit of ebb and flow: they’d go forward, they’d come back,” defence experts at Janes said.
On 8 April, another video was shared online showing damage to an area on the northern perimeter of the complex.
Sky News has located the strike to a building in an industrial zone in the north of the plant.
Five days later, Russia said that 1,000 soldiers from Ukraine’s 36th Marines Brigade had surrendered to its forces at the steel works.
‘Surrender’ of one of Ukraine’s most capable regiments
In a video message, the Ukrainian Azov battalion seemed to confirm that at least some had surrendered, but also claimed that others had successfully joined up with Azov fighters.
The Azov regiment is the Ukrainian battalion that has been fighting Russian forces in Mariupol. They are widely considered to be one of Ukraine’s most capable units, but many of its troops are affiliated with Ukraine’s far-right.
Footage of the alleged surrender was broadcast on Russian state TV. In it, soldiers can be seen walking with their hands up.
Sky News was unable to independently verify the contents of the footage, but was able to geolocate it to northern Mariupol.
The focus on Azovstal has heightened significantly in the past week as claims of victory in Mariupol emanate from the Russian side.
By this time, both Chechen forces and DPR units had announced assaults on Azovstal, prompting fears of a bloody showdown in the tunnels beneath the complex, where civilians are also trapped.
But experts at Janes say that while airstrikes and shelling have continued, there does not appear to have been any major battles at the facility.
“It does look like there’s been some fighting on the extreme eastern edges of the plant. But what we suspect is happening is that the Ukrainians are seeping out in small numbers and occupying positions on the outskirts of the plant in an attempt to harass the Russians,” they said.
They also question the motives that underpin public announcements of assaults on the site by Russian forces.
“There seems to be an effort to put the DPR at the forefront of seizing Mariupol, because it’s a DPR objective. And the Chechens, they have their own game. They have to sell the war back in Chechnya,” they said.
‘The most defensible position in town’
In fact, Janes say that at least 12 battalions are thought to be operating around the Azovstal area and believe it possible that the Russian Eighth Combined Arms unit is in charge of the operation.
But they say Russian forces would exercise caution when entering the plant.
“The place is a maze. There are also apparently underground tunnels running underneath – it’s a pretty terrible place to attempt to capture by force,” they said.
Janes say that the sprawling nature of the complex is likely one of the reasons it’s become the final stand for Ukrainian forces.
“It’s the most defensible position in town,” they said.
“You’ve got an entire flank covered by the sea, so you don’t have to worry about defending it as heavily. It’s a maze of industrial buildings and tunnels. This is naturally where any competent defender would seek to have their last stand.”
President Vladimir Putin cancelled the assault on Azovstal on 21 April, calling the plan “impractical” in a televised conversation with his defence minister.
Instead, he ordered a blockade of the perimeter so that “a fly can’t get through”.
Decision suggests ‘desire to free up Russian forces’
A defence intelligence update from the UK Ministry of Defence stated that President Putin’s decision “indicates a desire to free up Russian forces so they can be deployed elsewhere in eastern Ukraine”.
A video posted to Ramzan Kadryov’s Telegram channel on Friday claimed victory at Azovstal, but this has not been independently confirmed.
And local officials estimate that between 300 and 1,000 civilians are still trapped inside the plant’s tunnels alongside the remaining soldiers.
It is unclear exactly how the situation will progress at this stage.
But experts at Janes have predicted that the blockade will remain in place.
They said: “A siege seems the most likely outcome. Russians will continue using artillery and airstrikes to make life miserable inside.”
Writing and reporting: Victoria Elms
Digital production: Kieran Devine
The Data and Forensics team is a multi-skilled unit dedicated to providing transparent journalism from Sky News. We gather, analyse and visualise data to tell data-driven stories. We combine traditional reporting skills with advanced analysis of satellite images, social media and other open source information. Through multimedia storytelling we aim to better explain the world while also showing how our journalism is done.