The five kilogrammes bomb was hidden at the foot of a telephone booth at the main market entrance in Yala and detonated at 7.50am (9.50 Singapore time) by mobile phone, police said.

Separatist militants set off the bomb as three soldiers were patrolling nearby. All three are in a serious medical condition, while six shoppers nearby were also injured, none seriously.

Mr Somchai paid a one-day visit to the region on Tuesday, his first since becoming premier a month ago, telling reporters the number of separatist attacks had eased recently.

More than 3,400 people have been killed in rebel attacks by shadowy insurgent groups operating in the region since January 2004 and successive governments have struggled to quell the unrest.

Thailand's three far southern provinces were an ethnic Malay sultanate until mainly-Buddhist Thailand annexed the region in 1902, provoking decades of tensions. -- AFP