Lt. Gen. Igor Kirillov, commander of Russia’s forces responsible for nuclear, biological, and chemical defense, and a subordinate perished in an incident on Tuesday.

The Russian Investigative Committee reported that an explosive device, positioned on a scooter close to a residential building, caused the fatalities, according to The Associated Press.

RIC spokesperson Svetlana Petrenko stated in an official release, “Investigators, forensic specialists, and operational teams are on-site.” She added, “Investigations and searches are underway to determine all aspects of this crime.”

This is a developing story. Further updates will follow.