Cambodia and Thailand exchanged fire across their disputed border for a fourth day on Sunday, hours after US President Donald Trump announced the two Southeast Asian nations had agreed to ceasefire talks and threatened continued fighting would jeopardize their trade deals with Washington.

Following up on calls by President Trump, Secretary of State Marco Rubio spoke with his counterparts in both countries. But on Sunday morning, skirmishes erupted once more.

"I made it clear to [Trump] that Cambodia agreed with the proposal for an immediate and unconditional ceasefire between the two armed forces," Cambodian PM Hun Manet said after the phone call, adding that Trump's mediation "will truly help protect the lives of many soldiers and civilians".