A 21-year-old Russian soldier was found guilty of war crimes for killing an unarmed civilian and handed a life sentence by a Ukrainian court on Monday, in the first verdict of its kind since the invasion began three months ago.

The ruling came as President Volodymyr Zelensky warned elites gathered at the World Economic Forum in Davos that slow-walking military aid to Ukraine was costing thousands of lives, as he called for more weapons and even tougher sanctions against Moscow.

And as ferocious battles raged in eastern Ukraine, where Russia pummeled cities and towns in a bid to expand its hold on the Donbass region, a Russian diplomat in Geneva quit his post in protest over the war telling colleagues: "Never have I been so ashamed of my country."

Polish President Andrzej Duda (L) told Ukraine's parliament that 'business with usual' with Russia going forward was now impossible
Polish President Andrzej Duda (L) told Ukraine's parliament that 'business with usual' with Russia going forward was now impossible AFP / Sergei SUPINSKY

In a Kyiv courtroom, Russian serviceman Vadim Shishimarin looked on from a glass defence box as was sentenced in a trial followed around the world -- likely the first of many as Ukraine investigates thousands of alleged war crimes.

The sergeant from Siberia had admitted to killing a 62-year-old civilian, Oleksandr Shelipov as he was riding his bike in the village of Chupakhivka in northeast Ukraine.

He claimed he shot Shelipov under pressure from another soldier as they tried to retreat and escape back into Russia in a stolen car on February 28.

A verdict is due Monday in the war crimes trial of 21-year-old serviceman Vadim Shishimarin
A verdict is due Monday in the war crimes trial of 21-year-old serviceman Vadim Shishimarin AFP / Yasuyoshi CHIBA

Shishimarin apologised and asked Shelipov's widow for forgiveness, adding: "I was nervous about what was going on. I didn't want to kill."

But prosecutors stated he shot between three and four bullets with the intention of killing the civilian, and Judge Sergiy Agafonov sentenced him to life.

The sergeant was also found guilty of premeditated murder, which Agafonov said had been committed with direct intent.

Russian serviceman Vadim Shishimarin (in defendant's box) has admitted to killing a 62-year-old civilian
Russian serviceman Vadim Shishimarin (in defendant's box) has admitted to killing a 62-year-old civilian AFP / Yasuyoshi CHIBA

Shishimarin's lawyer Viktor Ovsyannikov said he would appeal the "most severe" verdict, arguing that "societal pressure" weighed on the decision.

International institutions are also probing abuses allegedly committed by Russian forces in places such as Bucha and Mariupol, which have become emblematic of the destruction and suffering of the war.

Graphic showing the advance of Russian troops in Ukraine as of March 13, 20:00 GMT.
Graphic showing the advance of Russian troops in Ukraine as of March 13, 20:00 GMT. AFP / STAFF

At the World Economic Forum in Davos, from which Russians have been barred this year, Zelensky made a fresh appeal for Western support.

He revealed that 87 people had been killed in a Russian attack earlier this month on a military base in northern Ukraine, in what would be one of the largest single recorded strikes of the war.

Western countries have sent huge amounts of weapons and cash to Ukraine to help it repel Russia's assault, and punished Moscow with unprecedented economic sanctions.

Smoke rises from an oil refinery after an attack outside the city of Lysychans’k in Ukraine's Donbas region
Smoke rises from an oil refinery after an attack outside the city of Lysychans’k in Ukraine's Donbas region AFP / ARIS MESSINIS

But Zelensky said tens of thousands of lives would have been saved if Kyiv had received "100 percent of our needs at once back in February", when Russia invaded.

Ukraine, he said via videolink, "is paying dearly for freedom and independence and for this struggle".

Later Monday, Zelensky said Russia has carried out nearly 1,500 missile strikes and over 3,000 airstrikes against Ukraine in less than three months.

Russian invasion of Ukraine
Russian invasion of Ukraine AFP / Sophie RAMIS

"Each time when we tell our partners that we need modern anti-missile equipment and modern military aviation, we are not just making a formal request," Zelensky said in his daily address to the nation.

"Our request means the lives of many people, who wouldn't have died, had we gotten the weapons that we are asking for."

Shortly after Zelensky's speech in Davos, US Secretary of Defense Lloyd Austin announced that 20 nations had pledged new arms, ammunition and other supplies to support Kyiv, while others were offering trainng for Ukraine's military.

Ramping up his demands that Moscow be cut off from the global economy, Zelensky also called in Davos for an international oil embargo on Russia, punitive measures against all its banks and the shunning of its IT sector.

He also urged all foreign companies to leave Russia -- which many have already done: US coffee giant Starbucks said Monday it would close all its 130 cafes there, following a similar move by McDonald's last week.

As Zelensky delivered his address, meanwhile, a counsellor at Moscow's mission to the United Nations in Geneva, Boris Bondarev, announced he was leaving his job after 20 years of diplomatic service in protest at Russia's invasion of its neighbour.

In the letter circulated to a number of diplomatic missions in Geneva and seen by AFP, he condemned the war as "not only a crime against the Ukrainian people but also, perhaps, the most serious crime against the people of Russia".

Western support has helped Ukraine in many areas hold off Russia forces which, after initially moving on Kyiv, are now focused on securing and expanding their gains in eastern Donbas and on Ukraine's southern coast.

The governor of Lugansk, in the Donbas region, said Monday that Russia has sent thousands of troops to capture his entire region and that the city of Severodonetsk was under massive attack, warning residents that it was too late to evacuate.

"At this point I will not say: get out, evacuate. Now I will say: stay in a shelter," Sergiy Gaidai said on Telegram. "Because such a density of shelling will not allow us to calmly gather people and come for them".

More than six million people have fled Ukraine and eight million have been internally displaced since the war broke out, according to the United Nations.

For the civilians left behind near the front, prayer is sometimes all they have left.

In the eastern city of Bakhmut, Maria Mayashlapak scanned the devastation of her home, where a missile destroyed her kitchen and cratered her vegetable garden.