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

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

It was the second armed confrontation since a Cambodian soldier was shot dead in May and marked a major escalation just 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, Thailand’s Defense Ministry said. The first clash Thursday morning occurred near the ancient Ta Muen Thom temple along the border between Thailand’s Surin province and Cambodia’s Oddar Meanchey province.

Here’s what to know about the dispute:

How the dispute began
Tensions flared in May when Thai and Cambodian forces briefly exchanged fire in a contested border area both countries claim. Each side said it acted in self-defense, and a Cambodian soldier was killed.

Although both governments pledged to de-escalate, tensions remained high as they imposed retaliatory measures. Thailand tightened border restrictions, allowing crossings only for students, medical patients, and essential cases. On Thursday, it sealed the border entirely.

Cambodia responded by banning Thai movies and TV shows, halting imports of Thai fuel, fruits, and vegetables, and blocking some of Thailand’s internet and power supplies.

Fighting sparks political turmoil in Thailand
Nationalist sentiments on both sides have fueled the conflict.

Thailand’s Prime Minister Paetongtarn Shinawatra was suspended on July 1 while under investigation for potential ethics violations over her handling of the dispute after a leaked phone call with a senior Cambodian leader.

In the June call, Paetongtarn referred to Cambodia’s former Prime Minister Hun Sen as “uncle” and criticized Thai military leadership, comments critics framed as undermining national sovereignty. Hun Sen, now Senate president, remains influential and was a longtime ally of Paetongtarn’s father, former Thai Prime Minister Thaksin Shinawatra, until tensions rose over the border issue.

The leak sparked public outrage and protests, and the ruling Pheu Thai-led coalition weakened after its second-largest partner, the Bhumjaithai Party, withdrew support, citing Paetongtarn’s perceived softness toward Cambodia.

Paetongtarn has apologized, arguing her remarks were part of a negotiating strategy. Former Defense Minister Phumtham Wechayachai has been appointed acting prime minister.

Border claims cause periodic tensions
Thailand and Cambodia share an 800-kilometer (500-mile) border, with disputes often stemming from a 1907 French colonial map. Cambodia has used the map to claim territory, while Thailand argues it is inaccurate.

The most violent clashes have occurred near the 1,000-year-old Preah Vihear temple. In 1962, the International Court of Justice (ICJ) awarded sovereignty over the temple to Cambodia, a ruling that has long strained relations. After further clashes in 2011, the ICJ reaffirmed its ruling in 2013.

Cambodia has again turned to the ICJ for resolution, but Thailand rejects the court’s jurisdiction.