Clouds of black smoke rise after an artillery strike is seen from a rebel-held position called “Shakhta” on March 31 near Avdiivka, Ukraine. At left, in the distance, a tall smokestack marks the location of a water-filtration plant caught in the crossfire. (Pete Kiehart/For The Washington Post)

Land mines and sniper fire, tank traps and unexploded shells have shut down Highway 20, the main artery into eastern Ukraine’s separatist stronghold of Donetsk. But despite the upheavals caused by two years of war, ordinary life along the route has struggled on.

As violence surges again, that could change.

One building near the desolate arc of tarmac is a water-filtration plant, staffed by 117 Ukrainian engineers and others. Hundreds of thousands of civilians on both sides of the front line depend on this crucial public utility, a symbol of resilience in an intractable conflict that has cost more than 9,000 lives.

Now, international cease-fire observers warn, renewed fighting between Ukraine’s army and Russian-backed separatists in the area threatens to destroy the plant, potentially triggering environmental havoc and a humanitarian emergency.

Although the war generates few headlines these days, ongoing hostilities remain deeply troubling to many, from civilians on the ground to leaders in the West. Last week, President Obama urged members of the Group of Seven to resolve the situation in Ukraine, admonishing, “We’re still seeing too much violence.”

A soldier smokes cigarettes in their underground sleeping quarters at a position called Shakhta on March 30 in Avdiivka, Ukraine. (Pete Kiehart/For The Washington Post)

In April, the cycle of strikes and counterstrikes flared to the worst levels seen since last summer. A new truce last month to mark the Orthodox Easter provided a respite for front-line communities, but that brief peace unraveled within days. On Sunday, the Ukrainian military said five of its soldiers had died in fighting just north of Donetsk — the second-highest daily death toll this year since the deaths of seven in fighting the previous Tuesday.

Artillery explosions around the government-held city of Avdiivka not only risk wrecking the nearby filtration plant and cutting off water for some 400,000 civilians. A direct hit could also disperse hazardous chemicals, including chlorine, in the already war-blighted area.

“It is important that the sides stop firing, especially close to residential areas and vital infrastructure,” said Alexander Hug, deputy head of the Organization for Security and Cooperation in Europe. An accidental release of the plant’s chemicals, he said, could result in “an environmental disaster.”

More than a ton of chlorine, which in concentrated forms is highly toxic, arrives daily at the plant. Damage to storage containers could expose up to 20,000 people to serious health problems, according to Voda Donbassa, which operates the facility.

Ukrainian commanders have forbidden their soldiers to return fire from separatists dug in around the plant, recognizing the magnitude of that risk as well as the prospect of a public-relations disaster for Kiev.

“The separatists use the water-filtration plant as cover to launch attacks on us,” said Vlad Yushkevich, 41, a platoon commander in Ukraine’s 58th Mechanized Brigade, which is stationed on the hillside opposite the plant. “We’re banned from firing back. The enemy knows this and uses it to his advantage.”

Yushkevich’s position, nicknamed “Shakhta,” or “the Mine,” overlooks Highway 20, its concrete bunkers and muddy warren of trenches offering a bleak vista of scrubby fields, bombed-out cottages and the first line of Russian-backed separatist fighters, as well as the plant. His men endure spartan conditions and monotonous routines, punctuated by sporadic bouts of combat.

“It’s a very tough situation right now,” he said as he sheltered behind a screen of camouflage webbing. “The Russian Federation keeps sending in new ‘humanitarian convoys.’ And we know what these are carrying — weapons and ammunition.”

His claims are supported by Ukrainian intelligence officials, who say that Russia has supplied separatist militants with dozens of artillery systems, more than 300 tanks and armored fighting vehicles and 6,800 tons of ammunition since the start of this year.

Oleksandr Turchynov, who heads Ukraine’s National Security and Defense Council, said last week that separatists had “significantly increased the intensity of shelling.” Avdiivka’s industrial district, known as the “Prom Zone,” bears the brunt of the war zone’s fiercest assaults, occasionally involving raids but generally taking the form of trench warfare.

The static conflict has locked eastern Ukraine into a sustained yet apparently contained cycle of violence.

More than two years after the war erupted, the battlefield — like the dynamics that govern it — has changed drastically, with a mass offensive now seemingly as remote as constructive political dialogue.

Even as Western leaders feel impelled to court the Kremlin’s cooperation over the impasse in Syria, Russia feels the pinch of sanctions imposed after its annexation of Crimea and clandestine invasion of Ukraine in 2014. The European Union is expected to renew those sanctions in a matter of weeks.

In rebel-held territory, many senior commanders regarded by Moscow as too ideological or headstrong have been relieved of their posts, often in bloody and suspicious circumstances. And last week’s dramatic prisoner swap involving Ukrainian pilot Nadiya Savchenko and two Russian special forces soldiers marked a moment of detente between Moscow and Kiev.

Yet the warring parties persistently trade blame for cease-fire violations. The latest round of talks among Ukraine, Russia, Germany and France, in April, failed to reach a breakthrough on such issues as the status of separatist-held territory and local elections. And brinkmanship persists in the Baltic, where Russian fighter jets keep buzzing U.S. military aircraft and warships while the United States boosts troop numbers along NATO’s eastern flank.

Last week, Russian President Vladimir Putin warned that Moscow would respond to U.S. moves in Europe and branded Washington’s missile-shield bases in Poland and Romania a direct threat to his country’s security.

On the ground, meanwhile, eastern Ukraine remains highly volatile. Some days, the line of contact is subjected to heavy fire from antiaircraft guns, mortars and grenade launchers. Other days, hot spots are eerily quiet. The net result is a region that continues to destabilize the post-Cold War order and impede Ukraine’s further integration with Europe.

A few miles west of the filtration plant and Avdiivka’s besieged Prom Zone lies a wood that was once a popular hunting spot. It is now a no-man’s land, riddled with land mines and the scene of random, fruitless skirmishes.

To Taras Lypka, 51, a conscript stationed here, no end to the deadly unrest is in sight.

“This is not a fighting war, this is a waiting war,” he said. “Give it a few years. Mind-sets will change, people will change. No one can win this with a military. Better just to hold the line and wait.”