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

Bangkok and Phnom Penh have been fighting over territory disputed since colonial power France drew the border between them more than a century ago.

Tensions along Cambodia's northern border with Thailand have been simmering since May, when a Cambodian soldier was killed in a clash with Thai forces.

Countries say they are prepared to discuss a ceasefire after US president talks to both leaders about border clashes

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.

Of course, trouble at the 508-mile (817 km) shared border is nothing new. For over a century, Thailand and Cambodia have contested sovereignty at various undemarcated points in the thick jungle punctuated with culturally-significant temples albeit with scant strategic or economic value.

Thailand and Cambodia exchanged heavy artillery fire for a second day on Friday as border fighting intensified and spread, while Cambodia's leader said Thailand had agreed to a Malaysian ceasefire proposal but then backed down.

The fighting intensified and spread to new areas despite international calls for a ceasefire. Read more at straitstimes.com. Read more at straitstimes.com.

Thai and Cambodian troops clashed in at least six areas along the countries’ shared 510-mile border on Thursday, killing one Thai soldier and nearly a dozen Thai civilians. The fighting—the second instance of armed confrontation between the two countries in almost two months—has sparked fears that the conflict could escalate into open warfare.

Thailand has rejected mediation efforts from third countries to end the ongoing conflict with Cambodia, insisting that Phnom Penh cease attacks and resolve the situation only through bilateral talks,