"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 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.

China has dismissed allegations that it was supplying weapons to Cambodia amid its ongoing border conflict with Thailand that has led to at least 33 people dying and hundreds of thousands displaced.

US President Donald Trump on Saturday announced that both the leaders from Thailand and Cambodia have agreed to meet immediately for ceasefire talks after three days of clashes

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 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.

Thai men's top seed Kunlavut Vitidsarn swept aside Malaysian Leong Jun Hao with a 23-21 21-7 win to march into the quarter-finals of the China Open on Thursday, while women's top seed An Se-young beat Sim Yu-jin 21-13 21-15 in an all-South Korean clash.