TORETSK, Ukraine — In the darkness of the cellar in the eastern Ukrainian town of Toretsk, the soldiers did not know how close the Russian glide bombs were landing. But the sudden change in air pressure that accompanied bone-rattling booms testified to the bombs’ destructive force as they tore into nearby buildings.

At dawn, during a lull in the attacks, several Ukrainian soldiers dashed out and saw a fire triggered by one of the bombs still raging through the ruins of a building about 150 yards away — the narrow margin between life and death.

There are many ways to kill and be killed in Russia’s war with Ukraine, but Ukrainian soldiers say that glide bombs are perhaps the most terrifying. They are free-fall bombs, many left over from the Soviet era, but now outfitted with pop-out wings that feature satellite navigation, turning them into guided munitions.

Referred to alternatively as “KABs” or “FABs,” they weigh 500 to6,000 pounds and are packed with hundreds of pounds explosives. A single blast can reduce a high-rise apartment building to rubble and obliterate even concrete fortifications.

“It is scary and very fast,” said Stanislav, a 28-year-old junior sergeant with Ukraine’s 32nd Mechanized Brigade, as Russian fighter jets unleashed the powerful guided bombs in the direction of his unit. “I just pray every time.”

In recent months, Russia has used the bombs to devastating effect, tilting the balance of fighting in eastern Ukraine in Moscow’s favor and allowing Russia to continue to make steady gains in the Donetsk region. The bombs have also allowed Russian forces to raze whole towns and villages with greater speed.

In the midst of the midsummer fighting around Toretsk, journalists from The New York Times were allowed to visit the town one night to witness the challenges that Ukrainian forces face as they try to hold positions under withering bombardments.

“The same thing every day,” said Jackson, a 29-year-old junior sergeant who commands a drone platoon for the 32nd. “We arrive at a position, they launch KABs, we hide, block our ears and open our mouths so as not to get a concussion,” he said.

Like Stanislav and others interviewed, he provided only his first name according to military protocol.

With Ukrainian forces almost pushed out of the small town of Niu-York a few miles to the south, the battle for Toretsk, a former mining town, is now underway.

Along with the Russian advance in the direction of Pokrovsk, a critical Ukrainian logistics center about 40 miles to the southeast, the enemy’s push into Toretsk is threatening to undermine the defense of the Donetsk region.

Ukrainian soldiers fighting in the hottest areas of the front say they are largely outgunned and outmanned. And Russia’s continuing ability to unleash unrelenting aerial bombardments, they said, continues to play a critical role in forcing them from even some of their most heavily fortified positions.

Finding a way to counter the threat remains a top military and diplomatic priority even as Ukraine engages in a bold gambit to flip the momentum of the war by mounting a cross-border incursion into the Kursk region of Russia.

Ukraine is hoping that the offensive will force Moscow to deploy more forces to defend that region, and thus ease the pressure along the eastern front by drawing in some of Russia’s better fighting forces.

So far, however, the Kremlin appears to be intent on maintaining its own offensive operations in eastern Ukraine and is pounding away at towns like Toretsk as relentlessly as ever.

It is a punch-and-counterpunch strategy for both armies — battered by years of brutal fighting, with each side wagering that their opponent will find themselves overstretched and newly vulnerable.

Ukraine has been developing its own long-range strike capabilities and is increasingly using domestically produced missiles and drones to target the airfields in Russia where the warplanes begin their bombing runs.

But Russian warplanes still managed to launch some 750 glide bombs in a single week in August, President Volodymyr Zelenskyy said.

Even Ukrainian soldiers accustomed to years of artillery bombardments shudder at the destructive power of the weapons.

A 152 mm artillery shell — which Russia fires by the thousands every day — contains a bit more than 13 pounds of explosive material. A commonly deployed glide bomb, the FAB-1500, is packed with more than 1,300 pounds of explosives.

Since the bombs do not use propulsion or give off a detectable heat signature, they are hard to spot. They can be launched from Russian warplanes dozens of miles behind the front lines, relatively safe from Ukrainian air defenses.

When Russian planes fly closer to the front, soldiers said, they are protected by Russian surveillance and attack drones that saturate the skies, searching for Ukrainian soldiers armed with portable antiaircraft missile systems.

“To shoot down a plane, you need to keep it in the sights for eight seconds and only then release the missile,” said Petro, 38, a senior sergeant of the 2nd Battalion of the 24th Mechanized Brigade. He previously fought around Toretsk and is now defending the nearby stronghold of Chasiv Yar.

Eight seconds in the open, he said, is an eternity. A Ukrainian defender can see the Russian jet streaking through the sky, he said, without being able to do anything to stop it because of the threat posed by the drones.

It is not clear how many civilians remain in Toretsk, but by the end of July there were believed to be fewer than 3,500, said Vasyl Chynchyk, the head of Toretsk military administration. More than 60,000 have been forced to flee the area, and those who remain live mostly subterranean lives.

“There is not one building which has not been damaged or destroyed,” Chynchyk said.

While the list of places obliterated by Russian forces continues to grow, experiencing the annihilation of a city in real time remains deeply shocking even for the soldiers who have witnessed countless scenes of desolation and destruction.

“When you drive into a ruined town, it’s like hopelessness,” Stanislav said. “This town is crying.”

A few hours later, his unit’s basement bunker was destroyed by Russian artillery. Fortunately, the soldiers said, they all escaped with only minor injuries and were setting up elsewhere to continue the fight.