A Thai soldier on the border with Cambodia has been wounded just hours after the UN called on the neighbours to establish a permanent ceasefire.
The two sides have blamed each other for starting the recent hostilities which began with four days of heavy fighting earlier this month.
The clashes left eight dead, displaced thousands and damaged the World Heritage-listed Preah Vihear temple.
The UN has backed efforts by regional grouping Asean to resolve the dispute.
A Thai military spokesman in Bangkok blamed Cambodia for the latest violence, saying hand grenades had been thrown across the border before dawn.
But he appeared to downplay the seriousness of the attack, describing it as a minor incident.
A hospital official in the border area confirmed to the BBC that one Thai soldier had been injured but he did not know how seriously.
The two heavily-armed militaries are ranged against each other across a 4.6-sq km (1130 acres) stretch of disputed land.
The BBC's Rachel Harvey in Bangkok says the news is further proof of how tense the situation is along the disputed border.
After hearing testimony from the foreign ministers from both countries, the UN Security Council called on Thailand and Cambodia to exercise "maximum restraint and avoid any action that may aggravate the situation".
The council's president, Maria Luiza Ribeiro Viotti, said there was "great concern" over the clashes.
Asean will hold a meeting of regional foreign ministers later this month to try to strengthen what is clearly a rather fragile ceasefire, our correspondent says.
Thailand opposes UN mediation, saying it can settled by the two states.
But Cambodia has described itself as being at war with Thailand and has suggested the UN send peacekeepers to the disputed area.