ROZADKY, Ukraine - Along Ukraine’s eastern front, soldiers man the sprawling maze of trenches and bunkers that form the backbone of defensive positions that stretch for hundreds of miles.

Carved into the hard earth during eight years of bloody fighting, these rugged outposts are occupied by soldiers who have weathered intense shelling and artillery strikes battling Moscow-backed separatists to a standstill.

“Farther from here is only the enemy,” said Andre, 23, an army officer who leads a unit at a deeply dug Ukrainian defensive position within range of enemy rifle fire. “It is only a matter of time before they send more of their forces.”

That moment may now have arrived for Andre and his men, as Russian forces launch a new onslaught that threatens to encircle Ukrainian positions on this contested land.

On Monday, Ukrainian President Volodymyr Zelensky announced that after days of amassing forces, the Kremlin has begun a large-scale offensive aimed at seizing what remains of Ukrainian-held territory in the country’s eastern Donbas region. The governor of the Luhansk region, Serhiy Haidai, announced Monday that the Ukrainian military had withdrawn from a town near the regional capital of Severodonetsk after weeks of intense Russian shelling.

Haidai urged civilians who remained near the fighting in and around the towns of Popasana and Kreminna to leave, warning them that “the Russians are killing everyone who’s against them on the spot.”

If the Russian offensive is successful, thousands of Ukrainian soldiers such as those dug into these front-line bunkers would be cut off from resupply lines. Soldiers and commanders interviewed here by The Washington Post in recent days said that if that happened, they would launch a fierce counteroffensive to fight their way out.

“We are fighting for our land, our country; forward toward victory is our only option,” said Volodymyr, a 22-year veteran of the Ukrainian army.

Reporters from The Post visited four front-line positions along Ukraine’s eastern front near the borders of the Donetsk and Luhansk regions. They traveled to within a half-mile of Moscow-backed separatists’ positions to assess the state of the war at these crucial Ukrainian defensive areas.

The Post was granted exclusive access to Ukrainian forces defending the eastern front on the condition that reporters not identify units’ specific locations or publish the full names of soldiers interviewed. While visiting the area on Saturday, nearby Ukrainian positions came under sustained artillery fire from areas controlled by separatist and Russian forces.

The landscape is dotted by a miles-long string of rudimentary military posts tucked into the rolling hills of the Donbas region. The thud of outgoing fire followed by the boom of exploding shells is a permanent feature here.

Rough-cut timber lines muddy trenches of the observation posts staffed in shifts, 24 hours a day. In one camouflaged dugout, a man on a heavy machine gun loaded with armor-piercing rounds waited; in another, a soldier scanned no man’s land through a periscope.

“Out here on the front lines, we rely on each other. Everyone understands the mission. We know the guys over there at the next position are doing their jobs to hold the line - we won’t let them down,” said Sergii, 44.

“If we lose here in the Donbas, the Russians won’t stop; they’ll come next for the rest of Europe,” he said, before returning to duty.

For any enemy tank attempting to break their defenses, a Ukrainian-made Stugna, an antitank missile, awaits just out of view. The system - capable of firing accurately up to five kilometers - is preferred by this unit over the shorter-range American Javelins and British NLAWs that they’ve only recently received from Western allies. “We are grateful for what we are getting from [British Prime Minister] Boris Johnson and the U.S., but it’s a little bit late,” said Andre, the unit commander.

“The enemy thinks we’re just kids with bows and arrows, but we’re actually armed with Stugnas, Javelins and NLAWS,” said Vadim, 22, an officer overseeing the units in this sector. “We’ve prepared, trained for this fight.”

Around the fortifications, artillery units roam Ukrainian defensive lines, firing a carefully counted number of rounds at preselected enemy positions. Facing an enemy with a near-endless weapons supply, ammunition and artillery pieces are precious commodities.

“We have to remind the enemy we are here and not going anywhere,” Vadim said.

Vadim was trained in Ukraine with instruction in the latest NATO military tactics and participated in multinational military exercises. He is part of a new generation of professional Ukrainian officers moving on from the Soviet military tradition that has long dominated here.

Those not on duty live underground, huddled in cramped quarters, protected from incoming missiles and Russian airstrikes beneath three feet of dirt. In the bunker, the air was thick with humidity after days of rain transformed fields across the region into a muddy morass.

Ukrainian soldiers who spoke with The Post described near-constant skirmishes as enemy reconnaissance units probed their positions for weaknesses, searching for future lines of attack to break through their defense. Enemy movements are met with artillery strikes and direct fire.

“The enemy keeps trying to advance toward our positions; it’s like they’ve lost their minds,” Vadim said. “We fire, and they keep coming.”

Those tactics have tied down Ukrainian forces stretched across the front, requiring the country’s strained military to commit valuable manpower and weapons to this area as their soldiers fight on multiple fronts.

There is little enemy movement across much of the area during the daytime hours, only pheasants darting through fields cratered by artillery strikes. With the arrival of Russian reinforcements to the region, fighters here expect the familiar rhythm that has defined years of trench warfare to become dramatically more active.

At a front-line position a few miles from heavy fighting in the town of Popasana, where Russian troops have made recent gains, a string of abandoned buildings offered protection from aerial bombardment and shelter from the high winds and rains. Despite the intense fighting, morale remains high here among the heavily armed men - and a handful of female soldiers.

Officers in a makeshift command center organized the hundreds of Ukrainian fighters and vehicles supporting them. Maps lined the walls that closely track battlefield developments next to desks cluttered with squawking radios.

Wired field telephones rang constantly with news of troop movements, and requests for fuel, ammunition and medical assistance, from units based across the front line. The conversations were brief, as a sole radio operator dealt with the flow of information.

“Our defensive positions have held the past eight years, but the enemy moves closer every day,” said the unit’s commander, Andre, who has battled separatist forces for much of his 12-year career in the army.

In late February, while fighting in the east, the commander’s hometown was occupied and his parents taken captive by Russian forces who threatened to execute them after learning their son was a Ukrainian army officer. Likely tipped off by others in the small village, the Russian soldiers searched the commander’s childhood home for proof of his military service, freeing his parents after they came up empty-handed.

In a makeshift military vehicle repair shop near the front, mechanics hammered away at the broken tracks of a tank and the mangled metal of self-propelled artillery brought back from the front lines. The pounding drowned out the frequent air raid sirens that sound at incoming attacks. Russian missiles and airstrikes have destroyed buildings near their position in recent weeks.

Military mechanics in teams work to repair mostly Soviet-era equipment. Some vehicles had been damaged by enemy fire; others needed replacement parts after hours of navigating muddy fields and potholed roads.

The limited pieces of Ukrainian military hardware were desperately needed at the front line. The priorities for repair shifted hourly for the solders as they responded to the immediate needs of those closest to the fighting. Crews worked nonstop to return tanks and fighting vehicles to service.

In a war that is nearing the two-month mark, most of the Ukrainian front-line positions have withstood the fierce assault, although attacks by Russian forces concentrated on a few key locations have revealed cracks in their defenses.

But in the makeshift auto shop, a group of grease-covered soldiers hunched over the engine hatch of a T-64 tank damaged by a mortar, in good spirits.

“We’re black and dirty,” one said. “But when the war is over, we’ll be squeaky clean.”

Eugene Lakatosh contributed to this report.