Ousted Prime Minister Thaksin Shinawatra has long provoked Thailand's government by rousing opposition at home. Now he's inflamed regional tensions by becoming an economic adviser to rival Cambodia.
At least three soldiers were killed during gunfights near a 900-year-old temple, whose ownership has been contested by both sides.
A disputed border region further strains the Thai government, which also faces protests at home.
Prime Minister Hun Sen, who has ruled for 23 years, won another five-year term Sunday. His party has overseen several prosperous years; critics say it stifles democracy.
Each side has domestic reasons to prolong the conflict.
Troops from Cambodia and Thailand have been amassing around Preah Vihear, an ancient temple claimed by both countries. UNESCO recently granted Cambodia's application for World Heritage Site status for the site.