Three people died and four others were wounded after a bomb exploded on a roadside in Thailand's troubled deep south, police said Tuesday.

The seven state railway employees were on their way to fix a section of track in Songkhla province, near the Malaysian border, which had been damaged in another bomb attack on Saturday.

The latest bomb was hidden around 200 metres from the site of the earlier explosion.

"We believe the bomb had been there since Saturday," said police colonel Chartchai Chanasit, adding that no other explosive devices had been found.

A low-level conflict has simmered in Thailand's south since 2004, killing more than 7,000 people, as rebels in the Muslim-majority region battle for greater autonomy from the state.

The area - heavily policed by Thai security forces - is culturally distinct from Buddhist-majority Thailand, which took control of the region over a century ago.

The explosions come after one person died and more than two dozen were wounded last month when a car bomb went off outside police accommodation.