Thailand and Cambodia clashed for a fourth day on Sunday, despite US President Donald Trump warning them they are risking potential trade deals with the US. The US president said on Saturday the leaders of the two countries had agreed to meet to negotiate a ceasefire.

Fresh cross-border clashes between Thailand and Cambodia broke out on Sunday hours after US President Donald Trump announced the two Southeast Asian nations had agreed to ceasefire talks.

The Thai warning came as the U.S. expressed its grave concern about the most serious fighting in years between the Southeast Asian neighbors. The U.S. and China compete for influence in fast-growing Southeast Asia, and both have good relations with Thailand and Cambodia.

Thailand, bound to America by a treaty from 1954, appears so far to have the upper hand against Cambodia after air strikes by American-made F16 fighters. Undaunted, however, the Cambodians, armed with Chinese-made rifles,

"The U.S. already flunked the test and that should be a wakeup call," a former senior U.S. State Department official told Newsweek.

Thailand favours bilateral negotiation rather than third-party mediation to resolve its military conflict with Cambodia, two Thai officials said, as fighting along their disputed border continued unabated.

Thailand bombed Cambodia with F-16 fighter jets on Thursday, as relations between the two countries imploded following clashes on a disputed border near the Emerald Triangle.