Thailand launched air strikes against Cambodia on Monday as a new wave of fighting erupted between the southeast Asian neighbors, marking the potential collapse of a peace plan presided over by US President Donald Trump just two months ago.

SURIN, Thailand -- Three Thai civilians were killed as heavy combat continued along the country's border with Cambodia, the Thai military said Thursday, marking the country's first civilian fatalities since the fighting resumed.

Thailand's curfew covers five districts of Trat province that neighbour Koh Kong. Residents are prohibited from leaving their homes between 7pm and 5am.

Fighting has flared up several times this year since a Cambodian soldier was killed in a May skirmish, as decades-old tensions over the border territory persist.

The escalation broke the ceasefire brokered in July by Trump who threatened to halt trade talks with the two countries unless they ended the fight.