KYIV—Around 31,000 Ukrainian soldiers have been killed since Russia launched its invasion two years ago, President Volodymyr Zelensky said, highlighting the scale of Ukraine’s sacrifice ahead of a decisive vote in the U.S. Congress on military aid to Ukraine .

“Every such loss is a great loss to us,” he said in a press conference Sunday. It was the first time Zelensky had offered a figure for Ukraine’s war losses, but he declined to name the number of wounded troops because he said doing so would help Russia understand how many were out of action.

The admission, which gives a lower number for Ukraine’s losses than most estimates cited by Western officials, comes as Ukraine marks two years of full-scale war with Russia and questions hang over continued military support from its Western allies.

Zelensky also said tens of thousands of Ukrainian civilians have died on territory occupied by Russia. “I don’t know how many of those dead were killed, murdered, tortured, deported,” he said. “We’ll know when we’re done with them, and with this Russia.”

Zelensky and top officials from his government demonstrated a united front on Sunday as they urged the U.S. to unlock critical aid packages and touted the successes of Ukraine’s growing military-industrial complex. The gathering in Kyiv on Sunday was a show of defiance amid doubts that Ukraine can keep fighting without that lifeline.

“I have faith in Congress, and I’m sure we’ll get positive news,” Zelensky said. “Otherwise I don’t understand at all what world we’ll begin to live in, but a different one for sure.”

Prime Minister of Denmark Mette Frederiksen, the Prime Minister’s husband Bo Tengberg and Ukrainian President Volodymyr Zelenskiy attend a memorial ceremony at the Field of Mars at Lychakiv Cemetery in Lviv, Ukraine Friday 23 February 2024. Ritzau Scanpix/Mads Claus Rasmussen via REUTERS

Zelensky said Russian forces assaulting Ukrainian positions on the frontlines are firing seven times as many artillery shells. He said he had spoken to U.S. congress members and made clear Ukraine’s urgent need for arms and ammunition.

“They know their support is necessary,” he said. “And they know what we need.”

The message from Zelensky comes as Ukraine seeks to address head-on the toughest challenges it faces in 2024. A law aimed at increasing recruitment to Ukraine’s battered military is expected to face a decisive vote in the country’s parliament in coming weeks, but it has been revised previously as there is no guarantee that it will pass.

Fresh from its seizure of Avdiivka in Ukraine’s east, Russia is pressing hard in several points along the front line, looking to deal Kyiv’s forces a psychological blow by recapturing villages in the south that Kyiv took back in a largely unsuccessful counteroffensive last year.

Russian President Vladimir Putin has indicated that he still wants to bring Ukraine under his control, and has pledged to continue the war. Zelensky on Sunday dismissed the prospects of peace talks with Russia.

“Can you speak with a deaf person?” he said of Putin. “Can you speak with a person who kills his opponents?” Zelensky said that, in time, Ukraine would propose a summit where Putin can “accept the fact that he lost this war.”

Questions hang not only over continued pledges of arms by Ukraine’s allies, but also the speed at which those are provided. Rustem Umerov, Ukraine’s defense minister, said only half of the West’s commitments aren’t delivered in the promised time frame.

Zelensky called for the provision of long-range missiles capable of striking targets deep inside Russian-held territory, and said that “a loss of time is a loss of life” when it comes to the pace of provisions by Ukraine’s allies.

U.S. national security adviser Jake Sullivan on Sunday reiterated the Biden administration’s calls for House Speaker Mike Johnson (R., La.) to push forward with a vote on Ukraine aid in his chamber , portraying Johnson’s decision as a crucial inflection point in the conflict.

“Now it comes down to a simple right or left turn, you know, one way is towards a vote that delivers Ukraine what it needs,” Sullivan said on NBC’s “Meet the Press.” “The other way is towards an outcome that Vladimir Putin would love to see, which is the United States not stepping up to its responsibility.”

Johnson and some other congressional Republicans have insisted that Ukraine aid should only pass as part of a larger package that also includes tighter restrictions at the U.S.-Mexico border, but House conservatives have already rejected a bipartisan Senate deal that combined those issues together and which would have unlocked some $60 billion in funding for Kyiv.

Meanwhile, Western sanctions have failed to stop Moscow’s war machine. Russia has reoriented its economy toward China and vastly increased military spending by almost 70% this year to $100 billion, more than at any point since the Soviet Union collapsed.

A made-in-Ukraine drone. PHOTO: JOSEPH SYWENKYJ FOR THE WALL STREET JOURNAL

Ukrainian officials are touting the work of their growing military-industrial complex, and in particular a major push to expand the production of drones that have come to play a pivotal role on the battlefield. Ukraine, unlike Russia, lacks an arms industry of a scale and sophistication required to sustain the war effort, but cheap drones can help offset the shortage of artillery shells from the West.

Mykhailo Fedorov, Ukraine’s minister of digital transformation, said the aim for 2024 is to produce one million explosive drones that can be used to target Russian positions. Makeshift factories are popping up all over Ukraine, churning out thousands of drones each month. This is in addition to a pledge of a million drones to Ukraine announced this month by Jens Stoltenberg , secretary-general of the North Atlantic Treaty Organization.

Write to Matthew Luxmoore at matthew.luxmoore@wsj.com