A Russian ultimatum to Ukrainian troops in Mariupol to surrender or die expired on Wednesday afternoon with no mass capitulation.

However, the commander of a unit believed to be holding out in the besieged city said his forces could survive just days or hours.

In a video, the commander of Ukraine’s 36th Marine Brigade, one of the last units believed to be holding out in Mariupol, asked for international help to escape the city’s siege.

“This is our appeal to the world. It may be our last. We may have only a few days or hours left,” said Major Serhiy Volyna in a video uploaded to Facebook.

“The enemy units are dozens of times larger than ours, they have dominance in the air, in artillery, in ground troops, in equipment and in tanks.”

Volyna spoke in front of a white brick wall in what sounded like a crowded room. Reuters could not verify where or when the video was filmed or who else might have been there.

Russia’s nearly eight-week-long invasion has failed to capture any of Ukraine’s largest cities.

Moscow was forced to retreat from northern Ukraine after an assault on Kyiv was repelled last month, but has poured troops back in for an assault on the east that began this week.

In the ruins of Mariupol, site of the war’s heaviest fighting and worst humanitarian catastrophe, Russia was hitting the last main Ukrainian stronghold, the Azovstal steel plant, with bunker-buster bombs, Kyiv said.

Ukrainian officials have said women and children are trapped in bunkers under the plant.

“The world watches the murder of children online and remains silent,” presidential adviser Mykhailo Podolyak wrote on Twitter.

Russia has been trying to take full control of Mariupol since the war’s first days.

Its capture would be a big strategic prize, linking territory held by pro-Russian separatists in the east with the Crimea region that Moscow annexed in 2014.

Russian-backed separatists said shortly before a 2 p.m. (1100 GMT) Wednesday deadline that just five people had surrendered.

The previous day, Russia said no one had responded to a similar surrender demand.

Ukraine announced plans to send 90 buses to evacuate 6,000 civilians from Mariupol, saying it had reached a “preliminary agreement” with Russia on a safe corridor, for the first time in weeks.

But none of those earlier agreements have actually succeeded on the ground, with Moscow blocking all convoys.

Once a prosperous port of 400,000 people, Mariupol has been reduced to a blasted wasteland with corpses in the streets and residents confined to cellars. Ukrainian officials say tens of thousands of civilians have died there.

The United Nations said on Wednesday the number of refugees who have fled Ukraine since Russia invaded on Feb 24 had exceeded five million. More than half are children.