A deadly fire that tore through a South Korean lithium battery factory in June was due to "gross" safety failures as the company raced to meet production targets, police said Friday.

Twenty-three people were killed at the Aricell lithium battery plant in the massive blaze, most of them Chinese nationals, in one of the country's worst factory disasters in years.

Aricell, a primary battery manufacturer, produced batteries for South Korea's military, but batches of its batteries had failed quality inspections in April — for the first time ever — and it was racing to redo those orders, plus meet June requirements, police said.