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

The deadliest conflict between the two nations in 14 years, now in its third day, extended to provinces about 200 miles south of where clashes first began.

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.