MARIUPOL, Ukraine — There are the booms that echo again, and parents know to tell their children they are only fireworks. There are the drones the separatists started flying behind the lines at night, dropping land mines. There are the fresh trenches the Ukrainians can see their enemy digging, the increase in sniper fire pinning them inside their own.
But perhaps the starkest evidence that the seven-year-old war in Ukraine may be entering a new phase is what Capt. Mykola Levytskyi coast guard unit saw cruising in the Azov Sea just outside the port city of Mariupol last week: a flotilla of Russian amphibious assault ships.
Since the start of the war in 2014, Russia has used the pretext of a separatist conflict to pressure Ukraine after its Westward-looking revolution, supplying arms and men to Kremlin-backed rebels in the country’s east while denying that it was a party to the fight.
Few Western analysts believe the Kremlin is planning an invasion of eastern Ukraine, given the likely backlash at home and abroad. But with a large-scale Russian troop buildup on land and sea on Ukraine’s doorstep, the view is spreading among officials and wide swathes of the Ukrainian public that Moscow is signaling more bluntly than ever before that it is prepared to openly enter the conflict.
“These ships are, concretely, a threat from the Russian state,” Captain Levytskyi said over the whir of his speedboat’s engines as it plied the Azov Sea, after pointing out a Russian patrol boat stationed six miles offshore. “It is a much more serious threat.”
Many Ukrainian military officials and volunteer fighters say that they still find it unlikely that Russia will openly invade Ukraine, and that they do not see evidence of an imminent offensive among the gathered Russian forces. But they speculate over other possibilities, including Russia’s possible recognition or annexation of the separatist-held territories in eastern Ukraine.
Ukrainians are awaiting President Vladimir V. Putin’s annual state-of-the-nation address to Russia on Wednesday, an affair often rife with geopolitical signaling, for clues about what comes next.
“I feel confused, I feel tension,” Oleksandr Tkachenko, Ukraine’s culture and information policy minister, said in an interview.
Mr. Tkachenko listed some invasion scenarios: a three-pronged Russian attack from north, south and east; an assault from separatist-held territory; and an attempt to capture a Dnieper River water supply for Crimea.
Russia, for its part, has done little to hide its buildup, insisting that it has been massing troops in response to heightened military activity in the region by NATO and Ukraine.
Ukrainian officials deny any plans to escalate the war, but there is no question that President Volodymyr Zelensky has taken a harder line against Russia in recent months.
Mr. Zelensky has closed pro-Russian television channels and imposed sanctions against Mr. Putin’s closest ally in Ukraine. He has also declared more openly than before his desire to have Ukraine join NATO, a remote possibility that the Kremlin nevertheless regards as a dire threat to Russia’s security.
Interviews with frontline units across a 150-mile swath of eastern Ukraine in recent days underscored the fast-rising tensions in Europe’s only active armed conflict. Officials and volunteers acknowledge apprehension over Russia’s troop movements, and civilians feel numb and hopeless after seven years of war. At least 28 Ukrainian soldiers have been killed in fighting this year, the military says.
“We live in sadness,” said Anna Dikareva, a 48-year-old postal service worker in the frontline industrial town of Avdiivka, where people scarcely flinch when shells explode in the distance. “I don’t want war, but we won’t solve this in a peaceful way, either.”
For much of last year, a cease-fire held.
Mr. Zelensky, a television comedian elected in 2019 on a promise to end the war, negotiated with the Kremlin for step-by-step compromises to ease the hardships of frontline residents and look for ways out of a conflict that has killed more than 13,000 people. But Russia’s insistence on policies that would essentially give it a say in eastern Ukraine’s future was unacceptable to Kyiv.
“The hope that Zelensky had to solve this issue, it didn’t happen,” said Mr. Tkachenko, the information minister and a longtime associate of the president.
Instead, the fighting has picked up again.
The Ukrainians’ labyrinths of trenches and fortifications along the roughly 250-mile front is by now so well established that in one tunnel near Avdiivka, the soldiers put up multicolored Christmas lights to spruce up the darkness. The town lies just a few miles north of the city of Donetsk, the separatists’ main stronghold.
At their hillside battle position, overlooking a separatist position in a T-shaped growth of trees, the soldiers described the sound of separatist drones that they said carried land mines dropped about a mile behind the line. Since December and January, they said, sniper fire from the other side increased, and they could see the separatists digging new trenches.
The lettering above the skull on their shoulder patches read: “Ukraine or death.”
“The enemy has activated lately,” said one 58-year-old soldier, nicknamed “the professor,” who said he would not give his full name for security reasons.
In Avdiivka, a volunteer unit of Ukraine’s ultranationalist Right Sector keeps a pet wolf in a cage outside the commander’s office. The commander, Dmytro Kotsyubaylo — his nom de guerre is Da Vinci — jokes that the fighters feed it the bones of Russian-speaking children, a reference to Russian state media tropes about the evils of Ukrainian nationalists.
Both sides have accused each other of increasing numbers of cease-fire violations, but Mr. Kotsyubaylo said that — to his regret — his fighters were allowed to fire only in response to attacks from the separatist side.
On the video screen above his desk, Mr. Kotsyubaylo showed high-definition drone footage depicting the quotidian violence taking place just 400 miles from the European Union’s borders. In one sequence, two of his unit’s mortar rounds explode around separatist trenches; a naked man emerges, sprinting. In another, an explosion is seen at what he said was a separatist sniper position; the clearing smoke reveals a body coated with yellow dust.
Asked what he expects to happen next, Mr. Kotsyubaylo responded: “full-scale war.”
Mr. Kotsyubaylo said he believed Russia’s troop movements north and south of separatist-held territory were a ruse meant to draw Ukrainian forces away from the front line. He said he expected Russia instead to launch an offensive using its separatist proxies in the self-declared Donetsk and Luhansk “people’s republics,” allowing Mr. Putin to continue to claim that the war is an internal Ukrainian affair.
“If Russia wanted to do it in secret, they would do it in secret,” Mr. Kotsyubaylo said of the massing troops. “They’re doing everything they can for us to see them, and to show us how cool Putin is.”
Under the peace plan negotiated in Minsk, Belarus, in 2015, both sides’ heavy weaponry is required to be positioned well behind the front line.
Ukraine’s artillery is now stationed in places like a Soviet-era tractor yard in an out-of-the-way village reached by treacherous dirt roads an hour’s drive from Mariupol. Col. Andrii Shubin, the base commander, said he was ready to send his artillery guns and his American-provided weapon-locating radar trucks to the front as soon as the order came.
Ukrainian officials say that they are not repositioning troops in response to the Russian buildup, and that any current troop movements are normal rotations.
On Monday, dozens of tanks and armored vehicles could be seen on the move in the southwest of the government-controlled area of eastern Ukraine’s Donetsk region. Soldiers relaxed on cots at a village train station under graffiti that used an obscenity to refer to Mr. Putin.
Around the region, from Mariupol’s fashionable waterfront to the shrapnel-scarred streets of Avdiivka, many residents said they were so exhausted from the war that they did not even want to consider the possibility that the fighting will flare up again.
Lena Pisarenko, a 45-year-old Russian teacher in Avdiivka, said she had never stopped keeping an emergency supply of water on hand in pots and bottles all over her apartment and her balcony. During the shelling at the height of the war, she created a ritual to keep her children calm: They would play board games and drink tea while three candles burn down three times. Then it was time for bed.
Another woman passing by, Olga Volvach, 41, said she was paying little mind to the recent escalation in shelling.
“Our balcony door isolates sound well,” she said.
Maria Varenikova contributed reporting from Mariupol, Ukraine.