KYIV, Ukraine: Half of all Western military support promised to Ukraine fails to arrive on time, complicating the task of military planners and ultimately costing the lives of soldiers in Russia's war, Ukraine's defense minister said Sunday.

Rustan Umerov, speaking at the "Ukraine. Year 2024" forum in Kyiv, said each delayed aid shipment means Ukrainian troop losses and underscored Russia's superior military might.

President Volodymyr Zelenskyy later told attendees at the event that 31,000 Ukrainian soldiers have been killed in action since Russia launched its full-scale invasion on Feb. 24, 2022. It was the first time that Kyiv has confirmed the number of its losses.

Commemorations to mark the second anniversary of the war on Saturday brought expressions of continued support, new bilateral security agreements and new aid commitments from Ukraine's Western allies. But Umerov said that they still needed to deliver on their commitments if Ukraine is to have any chance of holding out against Russia.

"We look to the enemy: their economy is almost $2 trillion," he said, adding that they use up to 15% of official and nonofficial budget funds for the war, which constitutes more than $150 billion. He said that whenever a commitment doesn't arrive on time, "we lose people, we lose territories."

During a press conference after the forum Sunday, Zelenskyy said four brigades did not take part in the country's counteroffensive against Russian forces because they hadn't received the equipment they were expecting.

"Can you imagine the numbers of guys who would have fought, who couldn't? The ones that had to sit and wait for the equipment they never received?"

The Ukrainian leader also confirmed plans for an international peace summit to tackle issues exacerbated by the war, such as nuclear or food security, in Switzerland in 2024. That would be followed by a potential invitation to Russian representatives to attend a second summit later in the year. However, Zelenskyy said Ukraine would not submit to a peace plan that did not serve its interests, and discarded the idea of direct negotiations.

"Is it possible to talk to a man who kills his opponents?" Zelenskyy said, referring to Russian President Vladimir Putin. "We will offer a platform where he can agree that he has lost this war and that it was a mistake."

Zelenskyy also spoke about ongoing fighting in northeastern Ukraine, where front-line conflict has intensified in recent months leading to the capture of the Ukrainian city of Avdiivka. He said that Moscow was using heavy artillery fire to put pressure on Ukrainian forces in the directions of Kharkiv and Kupiansk.

However, his speech remained defiant. "Will Ukraine lose in this war? I am sure that it won't. Our most difficult moment was on Feb. 24 two years ago. We have no alternative but to win. (...) If Ukraine loses, then we will not exist. We do not want such an ending to this fight for our lives."

Russian forces on Sunday appeared to be pressing on west of Avdiivka, the strategic city whose capture this month handed Moscow a major victory as fierce fighting rages on in eastern Ukraine.