The leaders of Cambodia and Thailand have agreed to meet to negotiate a ceasefire, according to a social media post by United States President Donald Trump on Saturday.

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 warned its conflict with neighboring Cambodia could “potentially develop into a war” as troops used rockets and artillery to shell targets along their contested border for a second

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