Thailand’s acting prime minister Phumtham Wechayachai warned that the escalating clashes with Cambodia could descend into a full war, as the two sides exchanged artillery fire in a second day of violence along the disputed border.

The Thai warning came as the U.S. expressed its grave concern about the most serious fighting in years between the Southeast Asian neighbors.

Why It Matters

The U.S. and China compete for influence in fast-growing Southeast Asia, and both have good relations with Thailand and Cambodia.

But China’s relations are particularly close with Cambodia, where the government has given the Chinese navy access to a naval base on the Gulf of Thailand, close to the disputed South China Sea, where China has extensive claims.

Thailand is a major non-NATO ally of the U.S., meaning it has a strategic working relationship with Washington.

What To Know

Firing erupted for a second day early on Friday at several points along the border and was particularly heavy near an ancient Khmer temple known as Ta Muen Thom, the state-run Thai News Agency reported.

“This present incident of aggression is escalating and could develop to the stage of war,” Phumtham told the media in Bangkok, The Guardian reported.

“However, right now we are still at altercation level, battling with heavy weapons. What we have done so far [is] to protect our land and [the] sovereignty of our nation.”

The two countries began fighting after a recent dispute over landmines erupted into exchanges of fire on July 24, with each side accusing the other of initiating the hostilities.

The Thai military sent F-16 jets to bomb Cambodian positions on Thursday while Cambodian forces fired BM-21 multiple rocket launchers into Thailand.

The U.N. Security Council is scheduled to hold an emergency meeting on the crisis later Friday in New York, AP reported.

The Thai Health Ministry said 15 civilians and one soldier had been killed and 46 civilians and 15 soldiers wounded in the clashes since Thursday. The Cambodian government has not given information on casualties.

Cambodia’s Khmer Times newspaper said Thai forces had attacked the Ta Muen Thom temple area, but Cambodian defenders had held them off.

In most areas, the Thai side of the border is more heavily populated than the Cambodian side, and more than 130,000 Thai civilians have moved to safety.

About 1,500 families in Cambodia’s the Oddar Meanchey province had been moved to safety, a provincial spokesperson said on Facebook. One villager had been killed there.

Cambodia’s former long-serving prime minister, Hun Sen, denounced in a post on the X platform what he called “Thailand’s military aggression” towards his country, “the ultimate consequence of which will be the suffering of the people.”

Thailand’s armed forces are much better equipped than those of its smaller rival, Cambodia.

The U.S. called for peace.

“The United States is gravely concerned by reports of the escalating fighting along the Thailand-Cambodia border. We are particularly alarmed by reports of harm to innocent civilians,” the U.S. State Department said in a statement.

“We strongly urge the immediate cessation of attacks, protection of civilians, and peaceful settlement of disputes.”

China also expressed its concern and said it wanted to “promote talks for peace in our own way and play a constructive role in promoting de-escalation.”

The clashes will be a major test for the Association of South East Asian Nations, or ASEAN, to which both Thailand and Cambodia belong. The 10-member regional bloc is aimed at promoting harmony and economic cooperation.

Malaysia is the chair of the grouping this year and its prime minister, Anwar Ibrahim, called on the rivals to “stand down” and resume talks.

What People Are People Saying

Cambodian defense ministry spokesperson, Lt. Gen. Maly Socheata, told reporters in Phnom Penh on Thursday: “All of Cambodia’s military operations this morning were acts of self-defence.”

Malaysian Prime Minister Anwar said on Thursday: “The least we can expect is for them to stand down and hopefully try to enter into negotiation.”

What Happens Next

One key question is whether outside powers will be able to press the two sides to stop firing and take up talks. The UN Security Council is due to meet later Friday to discuss the situation.