Bangkok. Armed clashes broke out Thursday between Thailand and Cambodia in long-disputed border areas, rapidly escalating months-long tensions.

The fighting included gunfire exchanges and shelling and rocket fire, which Thai authorities said killed at least nine Thai civilians and injured 14 others in three provinces. Thailand responded with air strikes.

It was the second armed confrontation since a Cambodian soldier was shot dead in May and a major escalation that came hours after the two countries downgraded diplomatic relations following a land mine explosion that injured Thai soldiers.

Clashes are ongoing in at least six areas along the border, the Thai Defense Ministry said. The first clash Thursday morning happened in an area near the ancient Ta Muen Thom temple along the border of Surin and Cambodia’s Oddar Meanchey province.

Here’s what to know about the dispute between the two Southeast Asian neighbors.

How the Dispute Began
The dispute flared in May after armed forces of Thailand and Cambodia briefly fired at each other in a relatively small, contested border area that each country claims as its own.

Both sides said they acted in self-defense. One Cambodian soldier was killed.

While the countries said afterward they agreed to de-escalate the situation, Cambodian and Thai authorities continued to implement or threaten measures short of armed force, keeping tensions high.

Thailand added tight restrictions at the border with Cambodia that stopped almost all crossings except for students, medical patients and others with essential needs. On Thursday, Thai authorities announced they were sealing the border entirely.

Cambodia also banned Thai movies and TV shows, stopped the import of Thai fuel, fruits, and vegetables and boycotted some of its neighbor’s international internet links and power supply.

Fighting Sparks Political Turmoil in Thailand
Nationalist passions on both sides have inflamed the situation.

Thailand's Prime Minister Paetongtarn Shinawatra was suspended from office July 1 to be investigated for possible ethics violations over her handling of the border dispute following a leaked phone call with a senior Cambodian leader.

In the June call, Paetongtarn referred to Cambodian former Prime Minister Hun Sen as “uncle” and criticized Thai military leadership, remarks framed by critics as disrespectful to national sovereignty.

Hun Sen was succeeded by his son Hun Manet in 2023 but remains influential as Senate president. He was a longtime friend of her father, Thaksin Shinawatra, a popular but divisive former prime minister, but they became estranged over the border dispute.

The leaked call sparked widespread outrage and protests. Paetongtarn's Pheu Thai party-led coalition also weakened when its second-largest partner, the Bhumjaithai Party, withdrew support, citing her perceived softness toward Cambodia.

Paetongtarn has apologized and argued her comments were a negotiating tactic. Her ally, former Defense Minister Phumtham Wechayachai, was appointed acting prime minister.

Border Claims Cause Periodic Tensions
Border disputes are long-standing issues that have caused periodic tensions between the two neighbors. Thailand and Cambodia share more than 800 kilometers (500 miles) of land border.

The contesting claims stem largely from a 1907 map drawn under French colonial rule that was used to separate Cambodia from Thailand. Cambodia has been using the map as a reference to claim territory, while Thailand has argued the map is inaccurate.

The most prominent and violent conflicts have been around the 1,000-year-old Preah Vihear temple.

In 1962, the International Court of Justice awarded sovereignty over the temple area to Cambodia. The ruling became a major irritant in bilateral relations.

Cambodia went back to the court in 2011, following several clashes between its army and Thai forces that killed about 20 people and displaced thousands. The court reaffirmed the ruling in Cambodia's favor in 2013.

Cambodia has again turned to the international court to resolve the border disputes but Thailand has rejected the court's jurisdiction.