For Ukrainian gun commander Oleksandr Kozachenko, the long-awaited U.S. ammunition can't come fast enough as he and his comrades struggle to hold off relentless Russian attacks.
His unit's U.S.-supplied M777 howitzer, which once hurled 100 shells a day at the encroaching enemy, is now often reduced to fewer than 10.
"It's a luxury if we can fire 30 shells."
Gunners with Kozachenko's 148th Separate Artillery Brigade and the 43rd Artillery Brigade, both in the Donetsk region, said they were desperate for more 155mm rounds for their Western cannons, which had given them an edge over Russia earlier in the war.
Resurgent Russian forces, which significantly outnumber and outgun the Ukrainian defenders, have been mounting multiple attacks across the eastern Donbas region in recent months and along the country's northeastern border last week.
The drive has marked an inflection point in the conflict spawned by Russia's full-scale invasion more than two years ago.
Russia has gained more territory in 2024 than it lost control of during Ukraine's much-hyped counteroffensive in the summer of 2023, according to Pasi Paroinen, an analyst with Black Bird Group, a Finnish-based volunteer group that analyses satellite imagery and social media content from the war.
Moscow's forces have claimed 654 sq km since the beginning of this year, outstripping the 414 sq km lost to Ukraine between June 1 and Oct. 1 last year, Paroinen said. Russia has gained 222 sq km of territory since only May 2, he added.
Russia's defence ministry didn't respond to a request for comment for this article, while Ukraine's military didn't immediately respond.
Colonel Pavlo Palisa, whose 93rd Mechanised Brigade is fighting near the key strategic city of Chasiv Yar, said he believed Russia was preparing a major push to break Ukrainian lines in the east. This echoed the commander of Ukraine's ground forces who said last week he expected the war to enter a critical phase over the next two months as Moscow tries to exploit persistent delays in weapons supplies to Kyiv.
"Without a doubt, this will be a difficult period for the armed forces," said Palisa, adding that he believes the Kremlin wants to capture the entire Donbas industrial region by the end of this year.
CITIES BRACE FOR RUSSIAN ADVANCE
Russian forces are gradually making inroads that could come to threaten several big cities in the east including Kostiantynivka, Druzhkivka, Kramatorsk and Sloviansk, which serve as key military hubs for Kyiv's war effort.
Some gains are striking fear in the heart of the hundreds of thousands of Ukrainians living in those Donetsk region cities as the enemy grinds ever closer.
"We live only for today," said 31-year-old school teacher Nina Shyshymarieva, standing with her young daughter outside a church in Kostiantynivka as artillery thundered in the distance.
"We don't know what will happen tomorrow."
Russian cannons are now easily within range of Kostiantynivka; the closest Russian position at the start of 2024 was about 20 km away, according to open-source maps that show shifting positions along the frontline. Now it is 14 km.
Shyshymarieva and the fighters on the frontline were among more than a dozen soldiers, commanders, residents and evacuation volunteers interviewed by Reuters in eastern Ukraine over the last two weeks. They painted a picture of deep uncertainty.
Much of the Donetsk region, which along with Luhansk makes up the greater Donbas area, is under daily bombardment, typically targeted at least a dozen times a day by Russian artillery or air strikes, according to regional governor Vadym Filashkin.
Ruins of homes, apartment blocks and administrative buildings are common sights in towns and cities.
Oleksandr Stasenko, a volunteer rescuer, said his team was receiving more evacuation requests particularly from Kostiantynivka and Kurakhove, another town further south, among other settlements.
Russian forces have encroached toward Kurakhove, too, advancing 2-3 km along the road running east from the town so far this year.
"Wherever the front line is approaching, people in those places are trying to leave as soon as possible," said Stasenko, adding that his group, East SOS, evacuates around two dozen a week, many of them elderly or infirm.
'TIME IS NOT ON OUR SIDE'
Ukraine has roughly 1,000 km of frontlines to defend in the east, north and south.
Some of the fiercest fighting in 2024 has centred on Chasiv Yar, which commands important high ground 12 km away from Kostiantynivka. It lies west of the devastated city of Bakhmut that Moscow seized last year after months of costly combat.
Russian advances near Chasiv Yar, and further south around the village of Ocheretyne, could drive wedges into territory relied upon by Ukraine's war planners for logistics, analysts said, because they would expose key roads to Russian fire.
A major highway leading west out of Kostiantynivka is already under threat. Cutting it off entirely would mean transit hubs further north, including Kramatorsk and Sloviansk, both numbering well over 100,000 people before the war, would lose a crucial supply line.
Russia's fresh assault on the northeastern Kharkiv region, which began on Friday, also risks diverting stretched Ukrainian forces from the eastern front, further compromising their ability to hold the line, according to said Emil Kastehelmi, another analyst at Black Bird Group.
"At the moment, it seems the goal of the (Kharkiv) operation is to cause confusion and tie remaining Ukrainian reserves to areas of lesser importance," he said.
Jack Watling, a senior research fellow at the London-based RUSI think-tank, said Russian forces would likely mount further attacks on northern and southern points of the frontline in order to stretch Kyiv's defences.
"Once Ukraine commits its reserves in these directions, the main effort will see the expansion of the Russian push in Donbas," he wrote in a May 14 commentary.
A new law strengthening Kyiv's mobilisation effort, which has been hobbled by public scepticism, takes effect on May 18. Experts and commanders say it could take several months before fresh recruits reach the front and reinforce exhausted troops there.
Even if Ukrainian forces can hold out until all the American ammunition and weapons get through to the front, the challenge ahead remains daunting, according to many of those fighting.
"I would say that it is unlikely that time is on our side, since a long war requires more resources," said Palisa, the colonel with the 93rd Mechanised Brigade, speaking hours after Russia launched its ground incursion in Kharkiv.
He added that it would be critical to impose as heavy a cost on Russia as quickly as possible.
"The enemy's resources, whether in terms of manpower or the materiel, cannot be compared with ours. It's extraordinarily large. That is why a long war, I think, is not in our favour."
