A motorcycle bomb exploded at the Muang Narathiwat District Office's parking area yesterday morning, injuring a passerby and three volunteer guards - Sayan Janwijit, 30, Abdullasi Lateh, 46, and Jirayus Kongsuwan, 23.
The injured passerby was Usman Dolojh, 31.
The bomb went off two minutes after a man parked the motorcycle on a pretext he was running some errands inside the district office.
The explosive, which weighed up to five kilos, was detonated by cell phone.
All victims are being treated at the Narathiwas Rajanagarindra Hospital.
Police are gathering evidence in a bid to track down the culprits.
