World Bulletin / News Desk

A four-year-old girl and her father were among three killed Tuesday when a bomb hidden in a motorcycle's fuel tank exploded outside a school in Thailand's insurgency-plagued south.

Two of the dead were father and daughter, local police detective Noppdol Kingthong told AFP, adding that the bomb was set off by radio control as the pair neared the school gate.

A 23-year-old man later died in  hospital and around a dozen other adults were being treated for injuries, according to a hospital worker who said the dead were Muslim.

Ethnic Malay insurgents in the kingdom's so-called "Deep South" have for years targeted schools and teachers, which are seen as symbols of Thai state power in the culturally distinct Muslim-majority region.

More than 6,500 people -- the majority of them civilian -- have been killed by rebels and Thailand's Buddhist-majority security forces since 2004.

Debris from the blast was strewn across the area while an abandoned child's school bag lay on the road.

UNICEF's Thailand representative Thomas Davin said the agency was "shocked and saddened" by the bombing. 

"No children nor any caretakers or education professionals should live or learn under fear of such attacks," he said in a statement.