LONDON (AP) — British police say a 3-year-old boy suffered severe burns on his face and arm during a suspected acid attack that investigators think was deliberate.

West Mercia police Chief Superintendent Mark Travis said police are working to identify the substance that burned the child on Saturday at a discount store in Worcester, England.

A 39-year-old man has been arrested on suspicion of conspiracy to cause grievous bodily harm. Three others were being sought for questioning Sunday and police released photos to generate public tips.

Travis said Sunday: “At this time we are treating this as a deliberate attack…. The incident will rightly shock the local community, and I would like to reassure local people that we are carrying out a thorough investigation.”

The boy is hospitalized. He has not been identified.