Opposition leader Abhisit Vejjajiva supports the General Border Committee as an instrument to resolve the border conflict with Cambodia.
However, he calls for caution over the planned withdrawal of troops from the disputed area near Preah Vihear temple.
He said Thursday the surrounding community, market and the Keo Sikha Kiri Svara pagoda in the 4.6 square kilometre disputed area must be cleared.
The locations of the Cambodian community, the market and the pagoda violated the memorandum of understanding covering the boundary that both countries signed in 2000, he said.
If third-party observers enter the disputed area and see the community, they might believe the area belongs to Cambodia. He said the occupation problem must be dealt with before third-party observers are allowed to enter.
Behind the News: Difficulties at the negotiating table
Mr Abhisit said he has conveyed his concern to the government.
He also complained about the government's failure to assert Thailand's ownership of the disputed area when a delegation of the United Nations Educational, Scientific and Cultural Organisation visited the area. That lapse could have implications for the International Court of Justice's decision over the disputed area next year.
Mr Abhisit insisted he supported the bilateral discussion on troop withdrawals through the GBC.
Meanwhile, Supreme Commander Gen Thanasak Patimaprakorn said he has nominated people to sit on the Thai-Cambodian Joint Working Group (JWG) that would work out details of the military withdrawal from the provisional demilitarised zone ordered by the International Court of Justice.
The JWG will comprise 17 members from each country. The Thai side will be led by Gen Worapong Sa-nganet, the chief-of-staff of the Royal Thai Armed Forces, said a military source.
The source said the Cambodian side may be headed by army deputy commander Hun Manet, who is the son of Cambodian Prime Minister Hun Sen.
Meanwhile, a mysterious loud bang was heard near a border village in Si Sa Ket province yesterday morning.
Some villagers thought it was an artillery round. Some metal debris was found scattered over the area.
Chokchai Saikaeo, chairman of tambon Sao Thongchai administration organisation in Kantharalak district, said the bang was heard about 11am. It sounded like an artillery shell, he said.
Shortly later, a piece of metal about 1 metre long and half a metre wide was found in a field at nearby Phum Srol Witthaya School. The same school was hit by artillery fire during border skirmishes between Thai and Cambodian forces earlier this year. Mr Chokchai said several more pieces of metal were found in other places following the bang. The military is investigating.