Six paramilitary rangers and four people were injured when a bomb hidden inside a motorcycle parked at the fresh market in southern province of Songkhla's Thepha district exploded on Saturday morning, Bangkok Post online reported.

Two rangers were in critical condition and admitted to a hospital nearby, police said. Police blamed separatist militants.

After the bomb attack, all security forces in Songkhla's districts of Jana, Thepha, Nathawee, Sabayoi and Hat Yai were ordered to be on high alert.

Since the resurgence of insurgency in 2004 in three southernmost provinces, Yala, Pattani and Narathiwat, altogether more than 4,000 local people, including about 250 soldiers and 240 police, have been killed and about 7,000 injured in more than 10, 000 violent incidents instigated by suspected secessionists.