Cambodia on Friday said that Thailand had broken a ceasefire agreed the day before by military commanders and endorsed by politicians in both countries, but that it would respect the deal, dpa reported.
Cambodian government spokesman Phay Siphan said Thai artillery fired a number of mortars early Friday near Ta Krabei temple on the north-western border. The temple is one of a half dozen sites that have seen exchanges of fire since April 22.
He said six shells landed on Cambodian territory.
"We are very sorry that Thailand has broken the agreement," he said. "It is a provocative act, but we restrain ourselves and we don't return fire. Cambodia is abiding by the (ceasefire) agreement."
Phay Siphan said Thai and Cambodian military commanders on the ground would meet to assess what had happened.
On Thursday Thai Prime Minister Abhisit Vejjajiva had called news of the ceasefire deal a "good sign for both countries."
Also Thursday, Thai Foreign Minister Kasit Piromya said Bangkok would welcome having Indonesian observers stationed at the Thai-Cambodian border to monitor the ceasefire.
Kasit said Thailand was "sincere and earnest" in its desire for peace, noting that Bangkok was a major investor and source of development assistance for Cambodia.
Kasit was speaking after talks Thursday with his Indonesian counterpart Marty Natalegawa. Indonesia, the current chair of Association of South-East Asian Nations (ASEAN), has been tasked with mediating between the two sides.
Cambodia has long said it wanted Indonesian border monitors, but a deal to place them stalled Monday when Thailand objected to some of the details in the agreement.
Bangkok has requested that the deal include the removal of Cambodian troops from temples along the border.
Fighting between the two ASEAN members broke out on Friday and has left at least 15 people dead and about 60 wounded on both sides. Each side has blamed the other for instigating the recent conflict.
International pressure to stop the fighting has increased in recent days, with the European Union on Wednesday describing the clashes as "very worrying" and calling for a peaceful resolution.
Cambodia said Wednesday that more than 31,000 of its citizens had fled the border region, while Kasit said around 50,000 Thai civilians had been evacuated from their villages.
Thailand has blamed UNESCO for escalating the tensions with its decision in 2008 to list the 11th-century temple of Preah Vihear as a World Heritage Site, despite Thai claims that a 4.6-square-kilometre area near the temple is still the subject of a five-decade border demarcation dispute.