The decades-old border dispute between the Southeast Asian neighbours erupted into military clashes several times last year, with fighting in December killing dozens of people and displacing more than one million on both sides.
The two countries agreed a truce on Dec 27, pledging to freeze troop movements and end the three weeks of clashes.
On Friday, Cambodia’s information minister Neth Pheaktra told AFP that the Thai military has started its “illegal annexation of Cambodian territory into Thailand, especially at Chouk Chey village”.
The Thai army, without mentioning any specific locations, said in a statement it had taken control of areas that had always belonged to Thailand but were “occupied” by Cambodia.
The Cambodian minister said Thai forces had damaged civilian buildings, installed barbed wire and shipping containers to create a “border fence”, and deployed to administer disputed areas.
“The unilateral assertion of Thailand’s sovereignty by force was also demonstrated by raising the Thai national flag,” the minister said.
A map provided to AFP by Cambodia’s information ministry shows Thai military presence in territory Cambodia claims as its own in the Chouk Chey area.
According to the Cambodian map, Thailand now controlled an area that, at its furthest point, is around 750m from a boundary line drawn by Phnom Penh through the village.
“Cambodia will not recognise any alteration of the boundary line resulting from the use of force,” Neth Pheaktra said.
The Thai army disputed Phnom Penh’s narrative and rejected recent media reports suggesting it had used force to seize Cambodian territory.
The locations, which the army’s statement did not name, “were originally places where Cambodian forces had deployed troops and where Cambodian civilians had settled, encroaching upon Thai sovereignty”, it said.
“Therefore, it is in fact Cambodia that had occupied parts of Thai territory,” the army added, arguing there was no “invasion or occupation of Cambodian land”.
Al Jazeera reported this week that Cambodia had lost territory to Thailand following their latest round of border clashes, with Chouk Chey “cut off by metal containers and barbed wire put up by the Thai military”.
Chouk Chey, whose residents were displaced by the fighting last month, is located in a patch of frontier land between Cambodia’s Banteay Meanchey province and Thailand’s Sa Kaeo province.
Thailand welcomed Cambodian war refugees to that area in the 1980s, with some families remaining long after fighting ceased in Cambodia’s civil war.
The Thai army said Cambodian civilians had encroached into Thai territory, “establishing communities and residences” illegally.
“Currently, Thai control and supervision of the area remains within Thailand’s territory, along operational boundary lines,” it said.
Cambodia says around 3,000 people lived in Chouk Chey before the clashes in December.
The two nations’ border conflict stems from a dispute over the colonial-era demarcation of their 800km border, where both sides claim territory and centuries-old temple ruins.