Preliminary talks between Thailand and Cambodia defense officials started on Monday in Malaysia ahead of a key ministerial level meeting on Thursday, as a fragile truce continues to hold a week after the two sides agreed on a ceasefire.

The ceasefire, which came after five days of border clashes between Cambodia and Thailand, was reached at a meeting in Malaysia last Monday, with help from the United States and China also observing.

The worst fighting between the Southeast Asian neighbours in over a decade included exchanges of artillery fire and jet fighter sorties, claiming at least 43 lives and leaving over 300,000 people displaced on both sides of the border.

The ministers of defense of both countries are due to hold a meeting of the General Border Committee to discuss how to maintain the ceasefire, authorities on both sides said.

The Thursday meeting will be observed by representatives from the United States, Chinna and Malaysia.

Mistrust between the two neighbours has lingered despite the ongoing talks, with the Cambodia defence ministry accusing Thailand in a statement of violating the ceasefire agreement by using excavators and laying barbed wire in a contested border area.

Thailand said both sides are maintaining their position without any significant movements.

But "there are reports that the Cambodian side has modified their positions and reinforced their troops in key areas... to replace personnel lost in each area," said Rear Admiral Surasant Kongsiri, a Thai military spokesperson.

Cambodia also demanded that Thailand releases 18 of its captured soldiers as soon as possible. Thailand said in a statement that the group are being treated well as "prisoners of war" and will be released after "a complete cessation of the armed conflict, not just a ceasefire."