The two countries exchanged heavy weapons fire for a second straight day on their disputed jungle frontier, the scene of a series of deadly gun battles in recent years.

Three Cambodian troops and one Thai soldier were killed Saturday, according to officials in the two countries, a day after three soldiers died on each side.

Cambodia accused Thailand of using 75mm and 105mm "heavy guns loaded with poisonous gas" and said in a defence ministry statement that Thai military aircraft flew "deep into Cambodia's airspace".

A Cambodian field commander, Suos Sothea, said the gas caused some soldiers who inhaled it to feel weak but did not cause serious injury. He also accused Thailand of using cluster bombs.

Thailand recently admitted using controversial Dual Purpose Improved Conventional Munitions during the February fighting but insisted it did not classify them as cluster munitions.

AFP