Police said unidentified gunmen killed four fruit traders in restive southern province of Yala on Tuesday, Thai News Agency reported.

Four traders, a couple and two men from the eastern province of Rayong, were killed at a house in Yala's Krongpinang district on early Tuesday morning.

According to preliminary police investigation, a group of seven gunmen in black outfits arrived in a pick-up truck, tied the victims' hands behind their backs and shot them dead.

Police initially believed it is the work of an insurgent group.

Police were investigating.

More than 5,000 people have been killed and more than 9,000 hurt in over 11,000 incidents, about 3.5 incidents a day, in Thailand's three southern border provinces -- Yala, Pattani, Narathiwat and four districts of Songkhla -- since violence erupted in January 2004, according to Deep South Watch, which monitors the regional violence.