The Indian manufacturer of cough syrups that Uzbekistan said last year had poisoned 19 children used a toxic industrial-grade ingredient rather than the legitimate pharmaceutical version, two sources with knowledge of the matter told Reuters.

The company, Marion Biotech, bought the ingredient — propylene glycol (PG) — from trader Maya Chemtech India, as reported by Reuters. But Maya did not have a licence to sell pharmaceutical-grade materials and "dealt in industrial-grade only," according to a source at the firm with knowledge of the Marion investigation.

"We did not know Marion was going to use it to make cough syrups," said the person, who declined to be identified while the case is investigated. "We are not told where our material is used."

The two sources said the syrup was made with industrial-grade PG, a toxic material widely used in liquid detergents, antifreeze, paints or coatings, and to enhance the effectiveness of pesticides.

"Marion bought commercial-grade propylene glycol," said a second source, an investigator, who declined to be named while the inquiry is ongoing.

"They were supposed to take Indian Pharmacopoeia-grade," the source added, referring to national standards for the composition of pharmaceutical products.

Marion also did not test the ingredient before using it in the syrups it sold to Uzbekistan, the investigator said.