WILLIAM BRANGHAM: The fighting is continuing at a grueling pace along the 900-mile-long front line in Eastern and Southern Ukraine.

Russia has put up stiff and deadly resistance to the Ukrainian counteroffensive.

With the support of the Pulitzer Center, special correspondent Jack Hewson, filmmaker Ed Ram, and produce producer Volodymyr Solohub on the war and its ghastly effects.

Two notes: We have blurred some imagery at the request of the Ukrainian military to disguise certain locations and sensitive equipment.

And a warning: Many details in this story are violent.

JACK HEWSON: Deep in the forest on the outskirts of Bakhmut, Ukrainian forces are back on the offensive.

We're on our way to an artillery position that.

We're having to move quickly through this undergrowth, making sure we spend as little time in the open, for fear of being identified by Russian reconnaissance drones.

Under threat from return fire, soldiers rush with a Soviet-era and prepare to fire on Russian forces.

Their target is a small village a few miles away occupied earlier this year just south of Bakhmut.

PETRO KACHAN, Soldier (through translator): In Klishchiivka Village, there was a command post and may be a machine gun position, and we were firing at it.

JACK HEWSON: As we talk to the gunner, we're cut short by incoming rounds.

PETRO KACHAN (through translator): Watch out.

Fire.

JACK HEWSON: Then, immediately, a command to fire.

Protected from shell fire, the command identifies its targets on the ground.

The situation is a reversal of three months ago.

Back then, the Ukrainians held the town as Russians encircled them and pounded them with artillery.

But now the Russians hold the center while the Ukrainians are making gains on the flanks.

IHOR SYDORENKO, Unit Commander (through translator): We were targeting the enemy's infantry unit's and we achieved our aim.

Some units were destroyed and some fled.

But Russians are well-trained and educated.

They use formulas to calculate their targets, so there artillery is very precise and they have more ammunition than we do.

JACK HEWSON: Tired, but determined, Ukrainian troops are pushing forward to take what is theirs, under pressure to make gains.

But Russian forces are learning to fight smarter.

And it's easier playing defense.

With approximately 100 square miles taken in three months, progress is slow and comes at great cost.

At field hospitals like this one, soldiers with horrifying injuries arrive every day, dozens of casualties, wounds inflicted by shrapnel, bullets, and land mines.

ANDRIY, Soldier (through translator): Everything is fine, for God's sake.

I'm fine.

JACK HEWSON: But everything is not fine.

Andriy has lost his foot and will be disabled for life.

We are at a stabilization point near to Bakhmut where Ukrainians are making gains, but it's still coming at a huge human toll.

This man just behind us has just his right leg blown off by an anti-personnel mine.

It is hard to comprehend his stoicism, showing few outward signs of pain, as the remnants of his right foot were sliced from his body and placed into a plastic bag.

Ukrainian military hospitals are actively targeted by Russian shells.

These medics risk their lives just by coming to do their work.

DMYTRO, Doctor (through translator): Artillery strike to our building, you can see it around.

We are walking in this place only in the basement, because the main reason, it's to be close to the front line.

Only in this case, we can treat heavy patients.

JACK HEWSON: Their job is to keep patients alive.

To outsiders, it is shocking.

But, for Rita, a paramedic, the blood has been normalized.

RITA, Paramedic (through translator): A regular person has not seen anything like this, but, with time, you understand you need to tune out and do your job very calmly, because on how composed you are a person's life depends.

JACK HEWSON: One might think all this suffering would push the Ukrainians to negotiate for peace.

But, right now, scenes like this just make them more furious.

Most want to fight on until they retake all their invaded land.

How long do you think you can keep doing this?

RITA (through translator): We will take it on no matter how much time it takes.

We hope it won't take too long.

JACK HEWSON: His injuries resulted from pushing into occupied ground.

Hundreds of thousands of Russian land mines are proving a deadly obstruction to Ukraine's counteroffensive.

As Andriy is evacuated to a city hospital, medics prepare for the next patient.

Since Kyiv's offensive push begin in June, there have only been modest gains.

Now, 100 miles north of Bakhmut, Ukrainian forces are coming under increased pressure to hold the line.

In Ukrainian-held Kupiansk, there has been a buildup of Russian forces over the last two weeks in one city.

Under forest cover, soldiers load a rocket battery on the back of a truck.

They race off to target a position a few miles from here.

Relaying the coordinates, taking aim, and they unleashed their first salvo.

They are trying to match Russian firepower.

MAN: In the past week, we have been working more actively than before.

They're trying to advance from a location I won't name.

We're trying to suppress them every day.

JACK HEWSON: They need to be quick as they switch positions, because they're always being watched.

That's seven rockets.

That is the biggest salvo they have fired so far.

So, they must have found something of value to be throwing that much weight at it.

With ammunition running low, the U.S. has started to supply Ukraine with controversial cluster munitions, which, as of last week, are being fired from these very forests.

VOLODYMYR, Soldier (through translator): Well, in comparison to what we use, the launch of one cluster munition is equal to four or five ordinary shells.

Sure, cluster munitions would be really helpful here.

JACK HEWSON: Most of the world's nations have agreed not to use cluster munitions, because unexploded bomblets litter landscapes for years after conflict, maiming innocent civilians.

Back at the stabilization point near Bakhmut, a casualty arrives.

His unit says he was killed by a Russian cluster munition, an example of how devastating these controversial weapons are.

Human rights groups deplore their usage by both sides.

What do you say to people who criticize Ukraine for wanting to use cluster munitions against the Russians?

RITA (through translator): To these critics, I can say come here and fight shoulder to shoulder with our boys, and then you can criticize.

JACK HEWSON: It is back to the battlefield and the grueling fight, the troops' resilience driven, as is their nation's, by a seething anger the every loss.

For the "PBS NewsHour," I'm Jack Hewson near Bakhmut, Ukraine.