Four men were arrested in connection with an apparent acid attack on a 3-year-old boy that occurred at a busy store in England on Saturday, police said.

Three men, ages 22, 25 and 26, were being questioned in London on suspicion of conspiracy to commit grievous bodily harm, West Mercia police said Monday. A 39-year-old suspect was arrested Sunday.

The attack took place around 2:15 p.m. at Home Bargains, a discount retail store in Worcester.

“At this time we are treating this as a deliberate attack on a 3-year-old boy,” West Mercia Police Chief Superintendent Mark Travis said in a statement. “The incident will rightly shock the local community and I would like to reassure local people that we are carrying out a thorough investigation to identify those responsible.”

Police said the boy was treated at the hospital for serious burns to his arms and face, and was later released. Authorities said the long-term medical implications for the child are unknown, but they hope he will not suffer life-changing injuries.

“It's an awful incident and we're really, really concerned about this,” Travis told Sky News.

Worcester City Council leader Marc Bayliss described the attack as “absolutely pure evil,” and urged anyone with information to come forward.

“Think if this was a member of your family, an innocent child, a 3-year-old probably scarred or damaged for life by this,” he told Sky News. “We need to bring the perpetrators to justice, and quickly.”

Fox News' Travis Fedschun and the Associated Press contributed to this report.