Russian President Vladimir Putin on Friday ordered his military to prepare options to retaliate against Ukraine for what he described as a drone attack on a student dorm that killed six people and wounded dozens, with 15 still unaccounted for.

Putin said the attack had struck the dorm in Starobilsk in Luhansk, a Russian-controlled region in eastern Ukraine. He said Kyiv’s military must have ‌known what it was targeting.

Ukraine’s military denied the Russian accusations and said it had struck an elite drone command unit in the area. It said that Kyiv complied with international humanitarian law.

Putin said in his own statement, which was carried by state television, that there were no military targets near the dorm.

“There are no military facilities, intelligence service facilities, or related services in the vicinity. Therefore, there is absolutely no basis for claiming that the munitions struck the building as a result of our air defence or electronic warfare systems.

“The strike was not accidental; it came in three waves, with ⁠16 drones targeting the same location,” Putin told officials.