President Volodymyr Zelensky of Ukraine said that a broad overhaul of the country’s military and civilian leadership was needed to reboot the war effort against Russia, suggesting that a major shake-up of his government was imminent.

Mr. Zelensky’s comments, in a broadcast on Sunday night, indicated that his plans would likely go beyond replacing the top military commander, Gen. Valeriy Zaluzhny. And they signaled a search for a new strategy among Ukraine’s leadership at a precarious moment, with depleted Ukrainian forces on the defensive and leaders in Kyiv waiting to see whether the United States will provide much-needed military and financial assistance.

“A reset, a new beginning is necessary,” Mr. Zelensky told the Italian media outlet Rai News. “I have something serious in mind, which is not about a single person but about the direction of the country’s leadership.”

Friction between the military and the civilian government represents the most serious schism in Ukraine’s leadership since the start of the war almost two years ago. The acrimony, which has been building for months, seemed to reach a breaking point last week, when Mr. Zelensky summoned General Zaluzhny for a meeting to tell him he was being fired, only to back off at least temporarily, according to Ukrainian officials familiar with the discussion.

Heightening the tension in Kyiv is the prospect of a new mobilization bill that could lead to the drafting of up to 500,000 troops. The bill, under debate in the Ukrainian Parliament, could be politically unpopular with the country’s war-weary citizenry.

Amid the speculation about his future, General Zaluzhny’s only public comment Monday was a cryptic Facebook message to a top deputy, General Serhiy Shaptala, reminiscing about collaboration through two years of war. “We can be sure that we will never feel shame,” Mr. Zaluzhny wrote.

The plans to reshuffle the civilian government signify a break with nearly two years of continuity in Mr. Zelensky’s wartime administration as he had mostly left in place ministers serving before Russia’s full-scale invasion. Before that, his government had been a revolving door of ministers.

With American aid stalled, political analysts have suggested that Mr. Zelensky might promote Ukraine’s ambassador to the United States, Oksana Markarova, who is seen as being in favor with the Biden administration, to a senior position in Kyiv. The U.S. government has been pushing for overhauls to strengthen anti-corruption safeguards on the billions of dollars in financial and military aid Ukraine is receiving during the war.

On Monday evening, the minister for veterans’ affairs, Yulia Laputina, submitted a letter of resignation to Parliament, without explanation. It was unclear if the resignation was related to the government reset Mr. Zelensky said he was considering.

Mr. Zelensky’s plans for a shake-up come after months of bloody, inconclusive fighting that have taken a toll on the nation’s mood, and dented his own popularity ratings. A poll by the Kyiv International Institute of Sociology in December found that 62 percent of Ukrainians trust Mr. Zelensky, down from 84 percent earlier in the war.

On the battlefield, Ukrainian forces are at perhaps their weakest point since the summer of 2022. Short of ammunition and personnel, they are struggling to hold back renewed Russian offensives across the front, with the epicenter of the fighting around the battered city of Avdiivka in the eastern Donetsk region.

Russian soldiers, using heavy cloud cover to evade detection by Ukrainian surveillance drones, managed to break into the northern outskirts of the city in recent days, according to Ukrainian soldiers in the area.

They are increasingly threatening a vital supply line and Ukraine’s control over the city. The fall of Avdiivka would represent the Russian forces’ most significant victory since they took Bakhmut in May, and it would open up new lines of assault in the Kremlin’s bid to seize the entire eastern Donbas region.

It could also free up resources for another Russian push taking place several hundred miles to the north, in the Kharkiv region.

Moscow has amassed more than 40,000 troops and hundreds of tanks and armored vehicles near Kupiansk, part of what Ukrainian military commanders said is an intensifying bid to retake territory in Kharkiv that Russian forces lost in a Ukrainian offensive more than a year ago.

The Ukrainian defense has been hindered by the suspension of vital American military assistance, with Republican lawmakers in the House of Representatives blocking repeated efforts to provide new funding.

The lack of assistance has not only resulted in a critical shortage of artillery and other weapons, but has made planning for the future exceedingly difficult.

At the same time, Ukraine is searching for a strategy to break out of the deadlock in the trench fighting, lest it be cornered into negotiations on a settlement on unfavorable terms, said Mykhailo Samus, a deputy director at the Center for Army, Conversion and Disarmament Studies, a military research organization in Kyiv. He said in an interview that the coming year might bring Ukraine’s last chance to shift the momentum of the war.

Even before the impasse in Washington, newly committed aid to Ukraine had dropped almost 90 percent between August and October compared with the same period in 2022, according to the Kiel Institute for the World Economy, a German research institute.

Senate Republicans and Democrats on Sunday unveiled a $118.3 billion bill that tied $60 billion in security aid for Ukraine to assistance for Israel as well as U.S. border security reforms. However, Speaker Mike Johnson, who had insisted on linking the disparate issues, has said the bill would be “dead on arrival” in the Republican-controlled House.

Mr. Biden urged lawmakers on Sunday to pass the legislation, saying that “if we don’t stop Putin’s appetite for power and control in Ukraine, it will go beyond Ukraine, and the cost to America will rise.”

Mr. Zelensky’s frustrations with General Zaluzhny have grown over the past year, as the fighting has bogged down in bloody, static trench warfare. But Mr. Zelensky has moved cautiously.

Replacing the military’s commanding general amid a Russian offensive along nearly the entire eastern front carries risks, as General Zaluzhny is well-regarded by soldiers and junior officers. His removal would be the most significant change in military leadership after the invasion.

“Soldiers see in him a leader, him and nobody else,” said an army major who asked to be identified only by his first name, Bohdan. Other officers have said that the army, respectful of hierarchy, would adapt quickly.

The general’s dismissal could also fuel concerns about instability in Kyiv’s wartime leadership and could be used by Russian propagandists to try to discredit Mr. Zelensky.

After General Zaluzhny, the highest-profile military leaders in Ukraine are Gen. Kyrylo Budanov, the head of the military intelligence agency, and General Oleksandr Syrsky, the commander of ground forces.

Mr. Zelensky may be trying to mute the potential backlash against firing General Zaluzhny by positioning it as just one move among a broader realignment.

“When we talk about this, I mean a replacement of a series of state leaders, not just in a single sector like the military,” Mr. Zelensky said in the broadcast on Sunday, when asked about reports that he planned to replace General Zaluzhny. “If we want to win, we must all push in the same direction, convinced of victory.”

Jake Sullivan, the U.S. national security adviser, said that the White House had been consulted about possible changes in Ukraine’s leadership and would not weigh in on personnel decisions.

“It’s the sovereign right of Ukraine and the right of the president of Ukraine to make his personnel decisions.” he said on CBS’s “Face the Nation.”

Maria Varenikova contributed reporting.