Some 31,000 Ukrainian soldiers have been killed defending the country in the two years since Russia launched its all-out invasion, President Volodymyr Zelenskyy said Sunday.

It’s the first time Kyiv has announced an official death toll of soldiers. Zelenskyy refused to give figures for the wounded and missing. “I don’t want to let Russians know how many of them are out of the war front,” he told a press conference in Kyiv.

According to Zelenskyy, Russian President Vladimir Putin’s forces have suffered 500,000 casualties in the war, including 180,000 soldiers killed. That compares with a figure of 315,000 Russian troops killed or wounded given by a senior U.S. Defense Department official earlier this month.

Zelenskyy also pleaded with Ukraine’s allies to speed up deliveries of aid to the war-torn country. “Delays mean loss of time, and loss of time means loss of our people,” Zelenskyy said.

“If we are strong, if we have weapons, we will not lose this war,” Zelenskyy said. “We will win. Because all of Putin’s steps backwards will definitely have a big impact on his society.”