The commander of the Department of Army Rangers 45, Col Rungroj Ananto, said martial law was imposed to allow a blockade to be established and the houses of four suspects to be searched in Tanyonglimo tambon.
Col Rungroj said the names and identities of the four suspects were being withheld while investigations were conducted. If the investigation found they were not involved in bombing the two railway lines in Rangae and Sungai Kolok districts, they will be freed, he said.
Tanyongmas chief engineer Adul Tolaema said equipment had been delivered and engineers had arrived to carry out repairs on the damaged tracks.
Repairs include the operations control system, the railway lines and re-connecting the lines.
The repairs should be completed by May 31 and train services on all routes should resume by June 1, Mr Adul said.
Wednesday's bombings halted southern train services at Tanyongmas in Rangae district.