The two neighbours have fought a series of deadly gunbattles in recent years in disputed jungle near ancient temples strung out along the frontier, which has never been fully demarcated, partly because it is littered with landmines.
The two countries regularly accuse each other of starting the clashes.
"All of sudden they fired at us," Thai Defence Minister General Prawit Wongsuwon told AFP after fighting resumed Saturday.
"It could be that they wanted to internationalise the situation to attract a third country (to intervene). We do not want to fight but have to retaliate when they fire at us," he said, calling for the resumption of bilateral talks to resolve the territorial dispute.
"We have to put pressure on them to go back to the meeting table," he said.
|Cambodian minister of health Mom Bun Heng offers mosquito nets to villagers who live near the Thai-Cambodia border|
Thai media reported that four Thai troops were wounded on Saturday but there was no official confirmation.
The fighting resumed at about 6 am (2300 GMT Friday) with rifle fire and shelling in the same area as Friday's deadly standoff, according to spokesmen on both sides.
It is the first serious outbreak of hostilities since February when 10 people were killed in clashes near the 900-year-old Hindu temple Preah Vihear, prompting UN Security Council members to call for a lasting ceasefire.
Cambodian Foreign Minister Hor Namhong described the new fighting as a "deliberate act of aggression" by Thailand.
Phnom Penh has called for outside mediation to help end the standoff, but Thailand opposes third-party intervention.
The two countries agreed in late February to allow Indonesian observers in the area near Preah Vihear, but the Thai military has since said they are not welcome and they have yet to be deployed.
The latest standoff, which left three soldiers dead on each side on Friday and more than a dozen wounded, took place near a different group of temples over 100 kilometres away from Preah Vihear.
Indonesia, which holds the rotating chairmanship of the Association of Southeast Asian Nations (ASEAN) regional bloc, has called for an immediate end to the violence.
"Indonesia, as current chair of ASEAN, strongly calls for the immediate cessation of hostilities between Cambodia and Thailand," Indonesian Foreign Minister Marty Natalegawa said in a statement on Friday.
The two sides blamed each other for Friday's clash, which lasted for more than six hours and prompted thousands of villagers to flee the border area.
Ties between the neighbours have been strained since Preah Vihear -- the most celebrated example of ancient Khmer architecture outside Cambodia's Angkor -- was granted UN World Heritage status in July 2008.
The World Court ruled in 1962 that the temple belonged to Cambodia, but both countries claim ownership of a 4.6 square kilometre (1.8 square mile) surrounding area.
Observers say the temple dispute has been used as a rallying point to stir nationalist sentiment in Thailand and Cambodia.
Thailand recently admitted using controversial Dual Purpose Improved Conventional Munitions during the February fighting but insisted it did not classify them as cluster munitions.
The arms are defined as cluster munitions by the global campaign group Cluster Munition Coalition (CMC), which condemned Thailand's use of the weapons.