Police are appealing for information following a suspected arson in Bitterne Park on Thursday evening (June 15).
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Police say they were called shortly before 8.55pm to a report of a suspected break-in at what they described as a "furniture store" on MacNaghten Road.
Officers say they attended and "saw a room inside the building had been set alight".
They said a 15-year-old boy, 14-year-old boy and 13-year-old boy, all from Southampton, were located inside and arrested on suspicion of arson and burglary, and are in police custody.
A 12-year-old boy was taken to hospital for treatment for minor injuries, and no other injuries were reported.
A force spokesperson said: “Officers investigating this incident would like to hear from anyone who was in the area at the time who saw anything that may assist our enquiries.
“Perhaps you were driving through the area and have dash cam footage that captured something suspicious?”
Anyone with information is asked to call 101 quoting 44230238099, or alternatively, go online and submit information. Alternatively, you can contact independent charity Crimestoppers anonymously on 0800 555 111 or via their website.