KYIV — Ukrainian forces are suffering from a shortage of artillery shells on the front line, prompting some units to cancel planned assaults, soldiers said this week, and stoking fears over how long Kyiv’s troops will be able to hold their ground against continuing Russian attacks.

The ammunition shortage is deepening the already palpable anxiety in the Ukrainian capital, as U.S. and European aid stalls and winter sets in.

“Our gunners are given a limit of shells for each target,” said a member of the 128th Mountain Assault Brigade, which is fighting in the southeastern Zaporizhzhia region.

“If the target there is smaller - for example, a mortar position - then they give five or seven shells in total,” he said, speaking on the condition of anonymity because of the sensitivity of the subject.

“The guys are tired - very tired,” he said. “They are still motivated - many people understand that they have no other choice.”

“But you can’t win a war only on motivation,” he continued. “You should have some kind of a numerical advantage, and with the weapons and weapons systems, it only gets worse and worse. How long can we last? It’s hard to say, but it can’t be long. Everyone understands this.”

Artem, 31, a gunner in the 148th Artillery Brigade who fires a 155mm howitzer, said his unit found a “dramatic” difference in stocks of shells after recently relocating from the southern front in Zaporizhzhia to positions in the east.

Artem said his unit was now firing just 10 to 20 shells per day at enemy targets, while previously it used an average of 50 shells, and sometimes up to 90. He spoke on the condition that he be identified only by first name in keeping with Ukrainian military rules.

“If the situation doesn’t change, or even worsens, we will not be able to suppress them and they will push us back,” Artem said. “What can you do with 10 shells per day? It is barely enough to respond to their advances - we are not even talking about attacking their positions.”

Insufficient supplies of shells have been a persistent problem for Ukraine since Russia invaded in February 2022.

Ukrainian President Volodymyr Zelensky confirmed the current shortage during his year-end news conference this week, though he insisted that the military was holding strong.

Earlier this month, Zelensky visited Washington, where he pleaded for lawmakers to free up $60 billion in aid that President Biden has proposed for Ukraine. No deal came through, however, as Republicans tied the aid to controversial border security measures. Days later, Hungarian Prime Minister Viktor Orban blocked $55 billion in European Union assistance to Ukraine.

The delays, which come on the heels of Ukraine’s unsuccessful counteroffensive this summer and fall, have created more unwelcome hurdles ahead of the winter holidays.

Russia continues to try to push forward on the southern and eastern fronts, and also to hammer Ukrainian cities with drone and missile attacks - many of which have been thwarted by Ukraine’s improved air defense systems. But those systems, too, depend on continued foreign support.

Ukrainian soldiers stationed at the front said they have not detected any sign that Russia is facing a similar shortage of artillery shells.

Although Moscow was forced to considerably slow its ammunition production in the first few months after the invasion, it has since managed to subvert hard-hitting Western sanctions and export controls and has reenergized its military production.

It has done this, in part, by exploiting loopholes in supply chains, while illicit smuggling networks have brought in key weapon components, including from the United States, by rerouting them through countries such as Turkey and Armenia.

A deal cut between Moscow and Pyongyang in September also provided critical help, with North Korea agreeing to supply Russia with much-needed missiles and shells. U.S. Ambassador to NATO Julianne Smith said this week that North Korea appeared recently to have delivered “1,000 containers of military equipment and munitions” to Russia for use in Ukraine.

Ukrainian Brig. Gen. Oleksandr Tarnavsky told Reuters that troops are facing ammunition shortages and that some plans have changed because of lack of supplies.

Lt. Gen. Ivan Havryliuk, one of Ukraine’s deputy defense ministers, declined to speak about the ammunition shortages, saying he did not have the authority to do so. A spokesman for the Defense Ministry did not respond to a request for comment.

The United States is Ukraine’s most important ally and Zelensky told reporters this week that he is “sure the U.S.A. won’t betray us.”

But Biden’s failure to secure the urgently needed funding for Ukraine before the end of the year showed that the White House simply cannot ensure everlasting support.

Biden, who previously insisted the United States would stand by Ukraine for “as long as it takes,” instead said earlier this month that it will support Kyiv for “as long as we can.”

The Biden administration has warned that barring passage of a supplemental spending bill, there is only enough money left to replenish U.S. stocks and deliver one remaining aid package.

“Once these funds are obligated, the department will have exhausted the funding available to us for security assistance to Ukraine,” Pentagon Comptroller Michael McCord said in a Dec. 15 letter to Congress.

NATO Secretary General Jens Stoltenberg has urged allies to work together to increase production for Ukraine.

Aware that it cannot rely forever on external aid, Ukraine is trying to ramp up its domestic weapons manufacturing. Its minister for strategic industries announced Wednesday that Ukraine plans to make 1 million first-person-view drones next year, along with thousands of other mid- and long-range weapons.

The explosive FPV drones have become key to Ukraine’s attack methods this year.

But in his own year-end news conference this month, Putin made clear that he is monitoring how Western aid for Ukraine has slowed.

“Today, Ukraine produces almost nothing,” he said. “Everything is brought in . . . for free. But the freebies may end at some point, and apparently it’s coming to an end little by little.

Some countries recently pledged tangible new military support for Ukraine.

On Friday, the Netherlands said it will transfer 18 F-16 fighter jets to Ukraine, although a timeline for that delivery was not made public. Japan, meanwhile, agreed to send Patriot missiles to the United States, in a move that would probably allow Washington to send more of the weapons to Ukraine. Kyiv relies heavily on the U.S.-designed Patriot systems to protect critical infrastructure in major cities.

But Ukrainian troops here say they need more of everything, and fast.

“We lack everything,” said a member of 128th Mountain Assault Brigade.

Ivan Zadontsev, a press officer for the 24th Separate Assault Battalion, also known as Aidar, said it had reduced firing by about 90 percent compared with last summer. His battalion needs 122mm munitions for Soviet-era howitzers; Western partners have tried to procure the ammunition for Ukraine throughout the war.

Aidar’s tactics changed around mid-autumn as deliveries of munitions diminished. Although the battalion has faced artillery shell shortages in the past, there are concerns now that reserves will not be replenished.

Like the 148th Artillery Brigade, Aidar is trying to hold defensive lines in the east, near the town of Klishchiivka, which Ukrainian forces liberated from Russian occupation in September. But Zadontsev said that to plan any further assaults “would be stupid . . . while the Russian army has artillery superiority.”

He said the worries over U.S. border policy that are holding up U.S. aid for Ukraine pale in comparison with the life-or-death urgency Ukrainians feel on the front. It is hard for him to imagine, he said, that anyone abroad can “even understand the situation at all . . . and how it’s critical right now.”

“I hope the U.S. government understands,” he added, “that keeping Ukraine safe with ammunition is much cheaper than rearming Poland and the Baltic countries if Ukraine will fall.”

Francesca Ebel in London and Serhiy Morgunov in Kyiv contributed to this report.