Ukraine’s forces have fought village-by-village to hold back a Russian advance through the country’s east, while the United Nations works to broker a civilian evacuation from the last Ukrainian stronghold in the port city of Mariupol.

An estimated 100,000 civilians remain in the city, and up to 1,000 are living beneath a sprawling Soviet-era steel plant, according to Ukrainian officials.

Ukraine has not said how many fighters are also present in the factory – the only part of Mariupol not occupied by Russian forces – but the Russians put the number at about 2,000.

Russian state news outlets reported that 25 civilians had been evacuated from the Azovstal steelworks, though there was no confirmation from the UN or Ukrainian officials.

Russia’s RIA Novosti news agency said 19 adults and six children were brought out of the plant, but gave no further details.

Video and images from inside the plant, shared with The Associated Press by two Ukrainian women who said their husbands are among the fighters refusing to surrender there, showed unidentified wounded men with stained bandages in need of changing; others had open wounds or amputated limbs.

A skeleton medical staff was treating at least 600 wounded people, said the women, who identified their husbands as members of the Azov Regiment of Ukraine’s National Guard. Some of the wounds were rotting with gangrene, they said.

In the video the women shared, the wounded men tell the camera they eat once a day and share as little as 1.5 litres of water a day among four.

Supplies inside the surrounded facility are depleted, they said.

The AP could not independently verify the date and location of the footage, which the women said was taken in the last week in the warren of passageways beneath the steel mill.

One shirtless man spoke in obvious pain as he described his wounds: two broken ribs, a punctured lung and a dislocated arm that “was hanging on the flesh”.

He said: “I want to tell everyone who sees this. If you will not stop this here, in Ukraine, it will go further, to Europe.”

Meanwhile, the bodies of three men were found buried in a forest not far from the Kyiv suburb of Bucha, the head of Kyiv’s regional police force said.

The men, whose bodies were found on Friday, had been tortured before they were shot in the head, Andriy Nebytov wrote on Facebook.

Ukrainian officials have alleged that retreating Russian troops carried out mass killings of civilians in Bucha.

Russian foreign minister Sergei Lavrov said in an interview that Russian and Ukrainian negotiators talk “almost every day.” However, he told Chinese state news agency Xinhua that “progress has not been easy.”

In Odesa – Ukraine’s third most-populous city and a key Black Sea port, a Russian rocket attack destroyed the airport runway.

Ukrainian news agency UNIAN reported several explosions were heard in Odesa on Saturday, prompting local authorities to advise residents to shelter in place.

Getting a full picture of the unfolding battle in the east has been difficult because air strikes and artillery barrages have made it extremely dangerous for reporters to move around.

Both Ukraine and the Moscow-backed rebels fighting in the east also have introduced tight restrictions on reporting from the combat zone.

Western military analysts have suggested that Moscow’s offensive in the eastern Donbas region, which includes Mariupol, is going much slower than planned.

So far, Russia’s troops and Moscow-backed separatist forces appeared to have made only minor gains in the month since Moscow said it would focus its military strength in eastern Ukraine.

Numerically, Russia’s military manpower vastly exceeds Ukraine’s. In the days before the war began, Western intelligence estimated Russia had positioned as many as 190,000 troops near the border; Ukraine’s standing military strength is about 200,000, spread throughout the country.

In part because of the tenacity of the Ukrainian resistance, the US believes the Russians are “at least several days behind where they wanted to be” as they try to encircle Ukrainian troops in the east.

With plenty of firepower still in reserve, Russia’s promised offensive still could intensify and overrun the Ukrainians. Overall, the Russian army has an estimated 900,000 active-duty personnel.

Russia also has a much larger air force and navy than Ukraine.

Hundreds of millions of dollars in military assistance has flowed into Ukraine since the war began, but Russia’s vast armouries mean Ukraine’s needs are nearly inexhaustible.

“We need an unlimited number of weapons,” Ukrainian defence ministry spokesman Col Oleksandr Motuzyanyk said.

In Mariupol, city officials have described dire shortages of food, water and medicine.

UN humanitarian spokesman Saviano Abre said the organisation is negotiating with authorities in Moscow and Kyiv but that he could not not provide details of the ongoing evacuation effort in Mariupol “because of the complexity and fluidity of the operation”.

Ukraine has blamed the failure of numerous previous evacuation attempts on continued Russian shelling.

The ferocity of the fighting has stunned the world. In the US, Pentagon press secretary John Kirby grew emotional on Friday as he discussed the “brutality” and “depravity” of the invasion ordered by Russian President Vladimir Putin.

“It’s hard to look at what he’s doing in Ukraine, what his forces are doing in Ukraine, and think that any ethical, moral individual could justify that,” Mr Kirby, a retired rear admiral, told reporters.

“It’s difficult to look at some of the images and imagine that any well-thinking, serious, mature leader would do that.

“So, I can’t talk to his psychology. But I think we can all speak to his depravity.”