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

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.

A Thai F-16 fighter jet bombed targets in Cambodia, both sides said, as weeks of tension over a border dispute escalated into clashes on Thursday that have killed at least 12 people, including 11 civilians.

Thailand is a major non-NATO ally of the U.S., while Cambodia is one of China's closest regional allies. The two countries began fighting after a recent dispute over landmines erupted into exchanges of fire on Thursday, July 24, with each side accusing the other of initiating the current hostilities.

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.

Residents in Thailand's Surin province bordering Cambodia ran for cover as the neighbouring countries exchanged fire, with weeks of tension over a border dispute escalating into clashes that have killed at least two civilians.

Tensions have bubbled between the two neighbors for months, flaring on Thursday as Cambodia and Thailand exchanged fire.