KYIV, Ukraine (AP) — The number of Russian troops killed or wounded in Ukraine has topped 1 million, military officials in Kyiv said Thursday, describing the huge price that Moscow has paid for its 3-year-old invasion.

"Even if you're on the ground, it's very difficult for you to count casualties," said Marina Miron, a postdoctoral researcher at King's College London.

Ukraine and Russia exchanged another group of ill and severely wounded servicemen on Thursday, officials from both countries said. All of the Ukrainian troops need treatment, Ukraine's President Volodymyr Zelenskiy said in a message on the Telegram messaging app that did not go into details on the numbers involved.