Separatist militants in Narathiwat had put up banners and spray-painted roads and bridges overnight, demanding police and soldiers leave the southern border provinces, police said on Monday.
Pol Capt Prachuap Nimruang, chief of a bomb disposal unit in Narathiwat, said the banners and spray-painted messages were found in 38 locations in 13 districts.
The messages, written in Thai and standard Bahasa Malaysia rumi script, demanded police and soldiers leave the deep South if Thailand wanted to see peace in the region.
Pol Capt Prachuap said the banners were probably put up and messages painted in the middle of the night.
Police officers were cautious that insurgents might be waiting to attack them if they went outside to inspect and clear up the areas.