Firefighters were digging through the burned remains of a house Saturday morning searching for the body of a child, the last member of a family killed in a catastrophic fire caused by a Russian drone attack.

Four bodies already lay in bags in the yard. Investigators had found the charred remains of the father in a corridor and the mother and two children in the bathroom.

Seven people in total died when Russian drones struck a fuel depot late Friday night in one of the most calamitous attacks yet on Kharkiv, the northeastern city that has suffered a series of missile strikes in recent weeks. Burning fuel poured down the street from the destroyed depot, setting a line of houses ablaze so quickly that two families were burned alive in their homes.

“The family was held hostage by the fire inside their own house,” Serhii Bolvinov, chief police investigator of Kharkiv, said after firemen and investigators dug for hours through the smoldering debris. “All of them were very badly burned, and DNA examination will be needed for the final conclusions.”

Oleksandr Kobylev, head of the Kharkiv regional police war-crimes department, said the Russians attacked with Iranian-supplied Shahed drones that struck shortly before 11 p.m.