A bomb exploded in front of a busy market in the southern Thai province of Songkhla, killing four people and wounding about 25, officials said.
The bombing came a day after at least 13 people were hurt when six bombs exploded Sunday evening in the city of Hat Yai, southern Thailand's tourist and commercial hub in the same province.
Monday's bomb in Sabayoi district, which exploded shortly after 4 p.m., had been hidden in a motorcycle parked in front of the market next to a railway station, said police.
Since early 2004, more than 2,200 people have been killed as a result of an Islamic insurgency that has swept over much of the southernmost provinces of Yala, Pattani and Narathiwat, the only ones with Muslim majorities in Buddhist-dominated Thailand.
The insurgency takes advantage of long-standing sentiment among southern Muslims that they are treated like second-class citizens in Buddhist-dominated Thailand. Attacks on civilians and officials in the three restive provinces close to Songkhla are seen as a move to drive out Buddhists from the area.