ZAPORIZHZHIA, Ukraine (NYTIMES) - Staff Sergeant Leonid Kuznetsov of the Ukrainian national guard is running out of time.

He and his comrades holding out in the Azovstal steel factory in Mariupol have only light weapons - machine guns, pistols - to defend themselves against Russian tanks, jets and artillery. They are holed up in a small, reinforced-cement bunker with peeling blue paint on the walls and about 2m of earth over their heads.

Even if the shelling that has been their constant companion for weeks comes to end with Vladimir Putin's order on Thursday (April 21) to end the assault on the factory, the Russian president's decision to blockade the last bastion of Ukrainian resistance "so that no fly can escape" could be a death sentence.

"I'm alive and healthy for now, but the situation is very difficult," said Kuznetsov, who is 25. "We're at the end of our food and water. We have about 1,000 civilians at the factory. I can't say how many soldiers we have. There are many, many wounded and not enough medicine. The smallest injury can be fatal; there are not even simple bandages."

The Russian military's destruction of Mariupol will be recorded in history as one of the singular calamities of Putin's disastrous war in Ukraine. A vivacious seaside town of about half a million people has been turned to a charred and pockmarked hellscape, the bodies of soldiers, civilians and their pets littering the once leafy avenues.

On Thursday, Russia's defence minister, Sergei Shoigu, announced to Putin that the ruined city was now fully under Russian control, save for the besieged steel plant. There are few buildings left standing and most of the city's residents, those who have not been killed in weeks of nearly incessant shelling, have fled.

The zone of Ukrainian control in Mariupol has narrowed to suffocating bunkers under the steel plant like the one where Kuznetsov and his fellow soldiers remain, running out of everything, including reserves of hope.

"We're hoping for help," he said. "If we don't get it, we won't make it out of this factory. We will die here with weapons in our hands defending Ukraine."

Kuznetsov communicated with a reporter by text using the chat app Telegram, and sent a short video of himself sitting in the bunker with a few fellow soldiers nearby. He has an Internet connection thanks to Starlink, the satellite Internet provider created by Elon Musk.

Kuznetsov chose to join the military after college because he thought that was what a man was supposed to do, his wife, Maria Kuznetsova, said in an interview. "It's his character," she said. "He thinks that a man must serve to protect his family."

Kuznetsova, 23, said she met her future husband when they were students at Mariupol State University. They married a few years later and now have a one-year-old son named David. Kuznetsov served for three years, then retired in December and filed an application to become a police officer.

Then, on Feb 24, the war broke out.

Kuznetsova said she repeatedly begged her husband not to rejoin the military, and initially thought she had talked him out of it.

"It's difficult to let your beloved man go," she said. "But every day he talked about it, and then quickly gathered up his things and went."

Kuznetsov said he was posted to different regions in the city before eventually being assigned to the Azovstal steel plant. For weeks it served as both a military base and a refuge for the families of soldiers and steel workers, as Ukrainian defenders in other parts of the city were killed or forced to retreat.

With no one else left to fight, Russian forces turned their entire might against the factory in recent days, pummelling it day and night with airstrikes, artillery and rockets.

Kuznetsov said more than 500 people were suffering from various injuries and there were many, many dead. A number of people sheltering inside have been killed by cave-ins caused by the shelling, he said.

He estimated that he and his fellow soldiers could hold out for another day, perhaps two.

"I ask the whole world to do everything possible to stop the military aggression against independent Ukraine," he said. "Punish everyone who is responsible for the military action on our territory."