A chemical plant in eastern Ukraine is reportedly sheltering hundreds of civilians from Russian shelling, setting the scene for a potential deadly showdown as Russian forces close in.
The situation on the ground is changing quickly, and concerns are growing for the safety of those trapped inside.
Russia-backed forces will reportedly reopen a humanitarian corridor for civilians to leave the Azot chemical plant, according to a separatist leader.
Here's what we know so far.
What's happening at the chemical plant?
The Azot plant is the largest chemical plant in Sievierodonetsk, an industrial city in Ukraine about 130 kilometres west of the Russian border.
Sievierodonetsk is the last pocket of Ukrainian land held in the Luhansk region.
The city has become the latest target of Moscow's military campaign after Russia failed to quickly capture Ukraine's capital of Kyiv.
Before the Russian war, the Azot chemical plant used to operate as a major producer of ammonia, used in agriculture as fertiliser.
At one time, it's believed 7,000 people were employed there.
Now, Ukrainian officials estimate about 800 civilians — including children and employees — are hiding in the chemical plant's underground bomb shelters.
Leonid Pasechnik, head of the self-proclaimed Luhansk People's Republic, said separatist forces had entered the plant but had been unable to dislodge Ukrainian fighters from the factory, the Tass news agency reported.
Inside, blasts of gunfire and shelling can be heard exploding above, and it is unlikely the bunkers will remain safe for much longer.
At least 70 per cent of Sievierodonetsk is now under Russian control, according to Ukrainian authorities.
Last week, Russian shelling caused a huge fire at the Azot plant, the governor of the eastern Luhansk region, Serhiy Gaidai, said.
He said the blaze started after oil leaked from damaged radiators at the plant and caught fire.
It is unclear whether there were any casualties.
Can the civilians escape?
It's getting harder and harder.
Governor Haidia said a mass evacuation was now "simply not possible" due to relentless fighting.
Russian forces have destroyed all the bridges into Sievierodonetsk, and have continued shelling the plant, he said.
He said some "access" to the city remained, but said damaged infrastructure was making it difficult for vehicles to get in and out, including trucks carrying humanitarian aid.
On Thursday evening, Interfax news agency reported Russia-backed forces will reopen a humanitarian corridor for civilians to leave the Azot chemical plant.
Why is this area important?
If Russia captures Sievierodonetsk and its twin city of Lysychasnk, it would give President Vladimir Putin full control over Luhansk, one of two provinces in the eastern Donbas region.
This victory would be a huge win for Russia.
That's partly because the Donbas is home to a large population of ethnic Russians who speak Russian as their first language.
For years, a deadly pro-Russian separatist movement has been underway in the region, with Russian proxies claiming Luhansk and Donetsk as independent "people's republics".
Controlling the Donbas would strengthen Russia's influence in the region, and possibly embolden Mr Putin to extend gains in the south.
How is the Azot chemical plant different to the Mariupol steelworks?
Russia's pounding of the Azot chemical plant echoes the bloody siege of the Azovstal steelworks, in the southern port of Mariupol.
There, hundreds of Ukrainian fighters held out for weeks inside the facility's large underground warren of tunnels and warehouses in an effort to protect hundreds of civilians hiding inside.
The bombardment eventually ended in mid-May, when those who surrendered were taken into Russian custody.
Although the battles appear similar, there are some key differences — none of which work in Ukraine's favour.
Unlike the steelworks, the Azot chemical plant does not have a labyrinth of sprawling networks buried underneath it.
It is much smaller, and there aren't as many places to hide.
The chemical plant is also nowhere near as protected — Governor Gaidai said the Ukrainian military did not strengthen defences at the plant due to the chemical risk.
