Firefighters were called to a blaze at The Swift complex on Rodgers Quay shortly after 4.15pm yesterday (May 22).
A NIFRS spokesperson said: “Firefighters were called to a derelict building on fire.
"They wore breathing apparatus and used two jets to extinguish the fire.
"The incident was dealt with by 5.30pm and the cause of the fire is believed to be deliberate ignition.”
Confirming the fire is being ‘treated as arson’, a PSNI spokesperson added: “There was no one inside the building and there were no reports of any injuries.
"Three boys have been spoken to by police in relation to the fire and have been reported to the Youth Diversion Officer.
"Anyone with information in relation to the fire is asked to contact police on 101, quoting reference number 1560 of 22/05/23.”