A Russian missile attack on a Ukrainian military training base killed at least 12 soldiers and wounded more than 60 others on Sunday, the Ukrainian military said, in a rare statement acknowledging casualties within its ranks.

Ukraine’s military did not disclose where the strike occurred, saying in a statement only that there was not a mass gathering at the time of the attack.

“At the time the air raid alert was announced, all personnel were in shelters, except for those who may not have had time to reach it,” Vitalii Sarantsev, a spokesman for Ukraine’s Ground Forces, said in an interview with Ukrainian news media.

Ukraine’s military does not typically disclose official casualty figures, which are treated as a state secret and are a highly sensitive topic in the country.

The strike on the training base came after what Ukrainian officials said was Russia’s largest combined overnight aerial assault on the country since the start of the war.

Russia launched 472 drones and seven missiles overnight, according to Ukraine’s Air Force. It said that the vast majority of the drones and three of the incoming missiles were intercepted, but that at least 18 targets were struck. The air force did not provide further details on what was struck.