If Ukraine's tenuous cease-fire comes to an end, it could well do so in the contested farmlands east of the strategic port city of Mariupol.

Fearing an attack from Russian-backed separatists, Ukrainian forces are digging defensive trenches and deploying heavy machine guns on hills to create a buffer just a few miles from Mariupol. Along the front line to the north, troops are hurriedly reinforcing checkpoints with cut logs and concrete. In town, officials are upgrading Soviet-era emergency plans.

“It all depends on the enemy and their actions,” says a Ukrainian commander who gave the name Sobol, speaking beside the new trench network. “We think they are using the truce to train forces and gather militarily in this direction, and it’s expected they will move.”

On the other side of the front line, however, there is little sign that pro-Russian rebels are building for an offensive. Few checkpoints exist along coastal roads and military hardware is hardly evident, at least up to a mile from the divided seaside village of Shyrokyne, which marks the front line.

“That’s just lies, they put out that information [of a rebel attack] to scare local citizens – they are expert in that,” says a separatist lieutenant colonel who gave the name Boxer. “We had an order to withdraw and we did it; now we only have light weapons here.”

While neither claim can be verified, and expectations are different on either side of this frigid winter landscape of barren fields, similarities also abound. Residents on each side wait in fearful expectation of an attack from the other. Both sides speak of "the enemy" in the language of disgust and hatred, threatening the permanent separation of Ukraine’s eastern industrial heartland. But both also desire an end to the fighting that has wrought so much destruction between once "brotherly neighbors."

Trading accusations

Both sides have made a show of pulling back heavy artillery guns. They claim they are adhering to a Feb. 15 cease-fire, even as they accuse their opponents of daily violations and using the relative lull to regroup and reinforce in a war that has so far left at least 6,000 dead.

Forces loyal to Kiev, the Ukrainian capital, say they are fighting “terrorists” who receive direct Russian support. The separatists say they are battling “fascists” who receive American and European arms. Both sides accuse the other of being pawns in a bigger battle between Washington and Moscow.

Many strategists see Mariupol as the final prize for the self-declared “people’s republics” of Donetsk and Luhansk, giving them a port to export goods and a closer link to Crimea, annexed by Russia last March.

Rebel leaders say they want to negotiate use of the port, not seize it by force. But on the fourth day of the cease-fire, after heavy fighting, they took control of Debaltseve, the railroad hub far to the north ­­– the latest in a series of victories.

With that in mind, Mariupol officials want to raise the price of any military strike so rebels don’t attempt it. Fortifications got under way last September, an effort that took on new urgency after a rebel rocket attack a month ago. It now takes the mayor just two minutes, 40 seconds to sound new warning sirens.

“The main goal for us is to slow the aggression of the Russian [rebel] gunfire,” says Yuri Khotlubey, the mayor of Mariupol. Civilians still remember when rebels controlled the city for a short time last spring, he says.

“People will not accept them to come back; they saw when they were here they were simple criminals, who blackmailed and raped, so they really aren’t welcome,” says Mr. Khotlubey. “The rebels are not enough to attack this city; they will need Russian troops to take it.”

Separatists deny those charges and the extent of Russian support for them – despite the array of widely matching uniforms, guns, and Russian military trucks with painted-over license plates and other military hardware. They accuse pro-Kiev forces of committing their own atrocities and abusing civilians.

“After all they [pro-Kiev forces] have done to us, we don’t consider them to be human beings,” says the rebel commander Boxer, a former coal miner who has fought throughout the rebellion. “This is just a species that has to be wiped out.”

Soviet-era bunkers

Such rhetoric is common to both sides, and, combined with images of destruction, have fed public fears.

“Of course we are scared. Only stupid and dead people have no fear, but there is no panic,” says Denis Gavrilov, the deputy head of civil defense in Mariupol. His office is dusting off Soviet-era emergency plans – designed to defend against a nuclear attack – and fit them to surviving rocket and artillery fire.

“We are creating a new system and Mariupol will be the example,” says Mr. Gavrilov. Lessons are being learned from a rebel barrage of at least 19 rockets on Jan. 24 that killed 31 people in the eastern district. Days later, the sirens were tested for the first time.

“A lot of people were not ready mentally for this,” Gavrilov says. “People of Mariupol for 25 years or more were friendly with the Russian Federation, and not ready to accept that a brotherly neighbor would attack us.”

There are decades-old bunkers for Mariupol’s 50,000 factory workers, But since January, basement shelters for the rest of the population of 450,000 have been cleared out. In a visit to one built beneath an apartment block during the rule of Josef Stalin in the 1950s, stairs lead down to a thickly walled labyrinth that smells of fresh green and white paint. Workers are adding a 250-liter water tank, sink, and a toilet, and later medical and food supplies.

Outside, a blue arrow painted on the wall points to the shelter. Notices addressed to “Dear Citizens!!” ask them to be ready with documents and cash, flashlights, batteries, and radios.

'Everybody is scared'

But there is little expectation on either side of this front line that Ukraine’s cease-fire will hold, and that the war is over.

“I was in Czechoslovakia in 1968, but it was nothing like this: We are killing one another, brother against brother,” says a man who fled the contested town of Shyrokyne four days ago to the next rebel-held village along the coast, Bezimenne.

The pensioner, who refused to give any name, described continued fighting and said bodies were still in the streets, where barely 30 people remained from a pre-war population of 1,000.

“I wish they would all die,” he says of the pro-Kiev forces, using the Russian word for the death of an animal.

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And yet just a few miles away on the opposite side of the front line, a similar disgust and fear was on the tongue of Dima, a 19-year-old fisherman, who lives 100 yards behind the newly dug Ukrainian trenches. Some 90 percent of the residents have fled already, and his family may join them.

“Everybody is scared,” says Dima, his eyes wide with fright. “I would rather have peace as soon as possible. Something should get us out of this hole.”