KYIV, Ukraine (AP) — At least 12 Ukrainian service members were killed and more than 60 were injured in a Russian missile strike on the location of a Ukrainian army training unit Sunday, according to a statement from the Ukrainian Ground Forces.

The strike occurred at 12:50 p.m. (0950 GMT), the statement said, emphasizing that no formations or mass gatherings of personnel were being held at the time. An investigative commission was created to uncover the circumstances around the attack that led to such a loss in personnel, the statement said.

The training unit is located to the rear of the 1,000-kilometer (620-mile) active front line, where Russian reconnaissance and strike drones are able to strike.

Ukraine’s forces suffer from manpower shortages and take extra precautions to avoid mass gatherings as the skies across the front line are saturated with Russian drones looking for targets.

“If it is established that the actions or inaction of officials led to the death or injury of servicemen, those responsible will be held strictly accountable,” the Ukrainian Ground Forces' statement said.

Meanwhile, Ukrainian drone strikes were reported deep in Russian territory Sunday, including in the Siberian region of Irkutsk, more than 4,500 kilometers (2,800 miles) east of Moscow. It is the first time that a Ukrainian drone has been seen in the region, local Gov. Igor Kobzeva said, stressing that it did not present a threat to civilians.

Other drone strikes were also reported in Russia's Ryazan region and the Arctic Murmansk region. No casualties were reported.

Russia’s Ministry of Defense said Sunday that it had taken control of the village of Oleksiivka in Ukraine’s northern Sumy region. Ukrainian authorities in Sumy ordered mandatory evacuations in 11 more settlements Saturday as Russian forces make steady gains in the area. Speaking Saturday, Ukraine’s top army chief, Oleksandr Syrskyi, said that Russian forces were focusing their main offensive efforts on Pokrovsk, Toretsk and Lyman in the Donetsk region, as well as the Sumy border area.

The strikes come amid continuing uncertainty as to whether Kyiv diplomats will attend a new round of peace talks proposed by Moscow for early next week in Istanbul. Ukrainian officials have called on the Kremlin to provide a promised memorandum setting out its position on ending the more than three-year war before the meeting takes place.

Moscow previously said it would share its memorandum during the talks.

In his evening address Saturday, Ukrainian President Volodymyr Zelenskyy called on Moscow to stop “playing with diplomacy” by withholding the document.

“At this point, we don’t have any clear information about what the Russians are planning to do in Istanbul,” he said.

“Of course, everyone in the world wants diplomacy to work and a real ceasefire to happen. Everyone wants Russia to stop playing with diplomacy and end the war. Everyone wants serious peace, and Russia must agree to this.”