From my findings, this claim seems true. According to UN News, on May 22nd, 2026, Ukrained sent out a drone strike into Starobilsk, which was thought to be a Russian occupied city in Ukraine. It turns out, Russians weren't the only ones hit, they hit a dormitory consisting of Ukrainian students. The United Nation News page is a very trusted source at is serves as one of the major news outlets for most of the United Nations. It turns out the Ukrainians hit by the strikes were young adults are teenagers from surrounding regions, who were living under Russian occupation. Ukraine has been receiving a lot of backlash over this, some even saying that Ukraine is a terrorist country. This claim is 100% correct and backed up by countless major news sources.
Source: https://news.un.org/en/story/2026/05/1167579