Police said a 20 kilogramme homemade bomb exploded near road No 42 in the Pattani provincial seat while a vehicle carrying border patrol police from Nakhon Si Thammarat was passing by.
The police had come to Pattani for a regular reassignment.
The explosion wounded four border patrol police.
In a related development, the authorities have arrested two men suspected of involvement in a bombing incident in Narathiwat on Sunday.
Narathiwat's Ra Ngae district police and army rangers have jointly searched a suspected location in Tan Yong Mat subdistrict and detained two suspects who may involved with the bomb attack.
The suspects, 21 and 19 years old, told police that they were behind the attack.