Deadly violence has flared up once again on thecontentious borderbetween Thailand and Cambodia, reigniting a long-running but little-known dispute. Thailand deployed fighter jets against Cambodian military targets on Thursday, as forces from both countries clashed along the border. The escalation came after a second Thai soldier in a week lost their leg in a landmine explosion. Diplomatic relations have deteriorated as a full-blown conflict threatens to break out, as both sides accuse each other of aggression. Thailand's health ministry said Thursday that 12 people, including 11 civilians and one Thai soldier, have been killed in clashes with Cambodian troops. A further 31 people have been injured, the ministry said. Cambodian authorities have not yet reported any fatalities on their side. Here's what to know about the disputed border. Tensions worsened in May when a Cambodian soldier was killed during a brief clash between Thai and Cambodian troops in a contested border area of the Emerald Triangle, where Cambodia, Thailand and Laos meet. Thai and Cambodian forces said they were acting in self-defense and blamed the other for the skirmish. Although military leaders from Thailand and Cambodia said they wished to de-escalate, both sides have since engaged in saber-rattling and reinforced troops along the border. Thailand took control of border checkpoints, imposed restrictions on crossings and threatened to cut electricity and internet to Cambodia's border towns. Cambodia in return stopped imports of Thai fruit and vegetables and banned Thai movies and TV dramas. Recent landmine explosions prompted both countries to downgrade relations with each other and recall diplomatic staff. The first soldier lost his leg in a landmine explosion on July 16. The second incident occurred Wednesday, when a blast injured five Thai soldiers, with one losing his leg. Thursday's violence marked a significant escalation. Thailand and Cambodia have had a complicated relationship of both cooperation and rivalry in recent decades. The two countries share a 508-mile (817-kilometer) land border – largely mapped by the French when they controlled Cambodia as a colony – that has periodically seen military clashes and been the source of political tensions. Cambodia has previously sought a ruling from the UN's International Court of Justice over disputed areas, including the site of the most recent clash. However, Thailand does not recognize the ICJ's jurisdiction and claims that some areas along the border were never fully demarcated, including the sites of several ancient temples. In 2011, Thai and Cambodian troops clashed in a nearby area surrounding the 11th-century Preah Vihear temple, a UNESCO world heritage site,displacing thousands of peopleon both sides and killing at least 20 people. The flare-up in May has had huge political ramifications in Thailand. Thailand's Prime Minister Paetongtarn Shinawatra wassuspended from dutiesin July after the leak of aphonecall she had with Cambodia's powerful former leader Hun Sen, in which she appeared to criticize her own army's actions in the dispute. Paetongtarn hails from a powerful dynasty and became Thailand'syoungest prime ministerlast year, at just 38. She could face full dismissal over the 17-minute phone call – in which she appeared to signal there was discord between her government and the powerful Thai military. The scandal and her suspension brought fresh uncertainty to the Southeast Asian kingdom, which has been roiled by years ofpolitical turbulenceand leadership shake-ups. Both sides' forces accuse each other of opening fire Thursday morning. Cambodia then fired rockets on Thai soil, Thailand said. A Thai fighter jet later dropped two bombs in Cambodian territory, Cambodia said. Cambodia's Defense Ministry condemned what it called "brutal, barbaric, and violent military aggression," accusing Thailand of violating international law. The ministry said a Thai F-16 had dropped two bombs on a road near the ancient Preah Vihear temple, a UNESCO world heritage site. "Cambodia reserves the right to lawful self-defense and will respond decisively to Thailand's violent aggression," the statement said, adding that the armed forces are "fully prepared to defend the kingdom's sovereignty and its people – whatever the cost." CNN has reached out to UNESCO for comment. Thailand's 2nd regional military command in the northeast said that F-16 fighter jets had been deployed in two areas, and it claimed to have "destroyed" two Cambodian regional military support units. Army spokesperson Col. Richa Suksuwanont said the strikes were aimed only at military targets. Thailand's acting caretaker, Prime Minister Phumtham Wechayachai, said Cambodia fired heavy weapons into Thailand without clear targets, leading to civilian deaths. The acting premier also said the conflict was not spreading into more provinces, according to Reuters. He added that no negotiation with Cambodia can take place until fighting along the border ends. Other countries have also weighed in, urging restraint and warning travelers against approaching the contentious border. At a briefing on Thursday, US State Department spokesperson Tommy Pigott told reporters that the US is "gravely concerned" about the violence. "The United States urges an immediate cessation of hostilities, protection of civilians, and a peaceful resolution of the conflicts," Pigott said. Additionally on Thursday, the United Kingdom's Foreign Ministry advised against "all but essential travel" within 50 kilometers of the Cambodia-Thailand border ineithercountry. CNN's Lauren Kent and Olivia Kemp contributed to this report. For more CNN news and newsletters create an account atCNN.com
