Milk poisoning that left three children dead and 36 people sickened in northwest China has been confirmed as an intentional food poisoning case, local authorities said Sunday.

Thirty nine people in Pingliang City, Gansu Province were sent to hospital after drinking nitrite-tainted milk on Thursday. Three children younger than two years old died, the youngest being 36 days old.

Suspects have been apprehended and interrogations and a continuing investigation is under way, said Zhu Lemin, an official in Pingliang Public Security Bureau.

Nineteen people have since been discharged from hospital as of Sunday, and the remaining 17 who are hospitalized are in stable condition, according to a statement form the Pingliang municipal government.