GEOFF BENNETT: Russia's full-scale invasion of Ukraine began four years ago today.

Europe's largest and most brutal conflict since the Second World War has claimed hundreds of thousands of lives, over 15,000 of them estimated to be civilians.

AMNA NAWAZ: European leaders met again today to pressure Russia as the many rounds of peace talks over the last year have produced few results and as beleaguered Ukrainians struggle to deal with the war's terrible toll.

Nick Schifrin reports.

And a warning: Some images in this story are disturbing.

NICK SCHIFRIN: In Kyiv this morning, a moment of silence for a nation in mourning, four years of war and sacrifice, of air raid sirens and cemeteries filled, four years of grief, of mothers who will never again see their children, the ultimate sacrifice made by more than 100,000 Ukrainian soldiers.

As the hell of this war rages, the front lines become so deadly, it's known as a 12-mile-wide valley of death; 1.6 million Russian and Ukrainian soldiers have either been killed, injured or missing since the start of the war.

That number will reach two million this spring.

More than 60 percent are Russian.

It is usually illegal to enter Russian military cemeteries.

But a woman posted this YouTube video from St.

Petersburg and a poem placed next to the grave of a 30-year-old Russian soldier: "No need to cry for me.

So many of us are dying here, countless of us.

The blood of boys is everywhere."

In Ukraine, it's been the deadliest year of the war.

The targets include kindergartens, one in Kharkiv, where parents and emergency workers ran to rescue 48 children, who all survived, also hospitals, its patients rescued on stretchers, nursing homes evicting the most vulnerable, and entire cities, Irpin, once a bustling Kyiv suburb, now burned out and silent, like the graves of its former residents.

No one nowhere has been spared the war's horrors.

Nearly four years ago, Olha Stiahluk lost her 21-year-old son, Yuri.

OLHA STIAHLUK, Mother of Fallen Ukrainian Soldier (through translator): What someone once considered to be a tragedy, a misfortune, now compared to this, to all this, what's happening here, you grasp what a terrible war this is.

NICK SCHIFRIN: Terrible especially from the sky.

We filmed this week in Izium, already once captured just 18 miles from the front.

Today, they try to protect themselves using nets to catch drones.

But 22-year-old Yulia Kondzha has nowhere to hide with her 1-year-old, Yuliana.

YULIA KONDZHA, Izium, Ukraine, Resident (through translator): There is no shelter.

We sit between the walls, where there are no windows, doors, so that it is a little safer.

My daughter is not afraid yet.

She is too young to understand.

But, still, the attacks have become much more frequent, much more.

NICK SCHIFRIN: Russia has also targeted Ukraine's energy infrastructure, plunging millions into freezing darkness during the coldest winter in over a decade.

That has helped Russia make slow advances even at enormous cost.

In four years, Russia has captured an additional 12 percent of Ukrainian territory, now controlling about one-fifth of the country, including most of the Donbass and the Zaporizhzhia nuclear power plant.

Those are the main territorial sticking points, as Russian, Ukrainian and American negotiators met last week for trilateral talks.

VOLODYMYR ZELENSKYY, Ukrainian President (through translator): One thousand and four hundred and sixty-two days of the full-scale war.

Of course, we all want the war to end, but no one will allow Ukraine to end.

We want peace, strong, dignified, lasting.

That is why there are so many rounds of negotiations and a battle for every word, for every point, for real security guarantees.