Two Russian missiles struck a Ukrainian training ground on Thursday morning, according to the Southern Operational Command.

The group said the base is “located in the rear and relatively calm part” of Ukraine without specifying the location.

According to the update, there were casualties despite precautionary measures, though the exact number of casualties remains unclear.

“Due to enemy fire, despite the alert, moving to shelter and other safety measures taken, it was not possible to completely avoid losses. The relevant emergency services are working on the scene,” the update says.

“The wounded are being promptly provided with all necessary medical assistance,” it adds.

The Military Law Enforcement Service is conducting an internal investigation into the incident, it wrote.

The group said the attack took place during a “massive combined strike on Ukraine.” Ukraine’s Air Force reportedly detected 37 missiles, including 28 ballistic missiles, and 320 drones overnight in its morning update.

The attack mainly targeted Ukraine’s energy facilities, prompting blackouts across the country. Officials confirmed that gas production sites in the Poltava region were shut down following the attack.

Russian attacks in recent months have slashed Ukraine’s gas production by over half.

Euromaidan Press reported that the latest attack was the sixth since June.

On Aug. 12, a Russian missile armed with cluster munitions hit a training unit of Ukraine’s Ground Forces, killing one soldier and injuring at least 23 despite evacuation efforts.

On July 30, another training unit was hit by a Russian missile, killing three and injuring at least 18.

On June 1, a missile strike killed at least 12 troops and wounded over 60, leading to the resignation of Ground Forces commander Mykhailo Drapaty.