The blast came two days after Thailand's cabinet approved a three-month extension of emergency powers in the country's troubled southern region.
The emergency powers, which have been in place since July 2005 and are renewed by the cabinet every three months, cover Yala, Pattani and Narathiwat - the only Muslim-majority areas of the Buddhist country.
The three provinces have been hit hard by an armed anti-government campaign has left more than 3,000 dead since 2004.
The region's Muslims have long complained of mistreatment and discrimination.
Legal immunity
The state of emergency allows the government to impose curfews, prohibit public gatherings, censor and ban publications, detain suspects without charge, confiscate property and tap telephones.
It also gives officials legal immunity for acts - sometimes including killings - carried out under its provisions.
Human-rights activists have criticised the continued use of emergency rule, saying it has failed to contain violence and has worsened the situation by allowing violations of constitutional rights.