A Thai fighter jet dropped bombs on Cambodian military targets along their disputed border on Thursday, as armed clashes between the two Southeast Asian neighbors killed at least nine civilians, in adramatic escalationof tensions that threatens to erupt into a broader conflict. The violence comes a day after a Thai soldier lost his leg in a landmine explosion, an incident that cratered relations between Bangkok and Phnom Penh to their lowest level in years. Thailand has since closed all border crossings with Cambodia. Thailand's 2nd regional military command in the northeast said in a post on Facebook that F-16 fighter jets had been deployed. It also claimed to have "destroyed" two Cambodian regional military support units. Thailand's deputy Army spokesperson Col. Richa Suksuwanont said the strikes were aimed only at military targets. Cambodia's Defense Ministry confirmed that a Thai F-16 fighter jet had dropped two bombs on a road near the ancient Preah Vihear temple, a UNESCO world heritage site. It condemned what it called "brutal, barbaric, and violent military aggression" and accused Thailand of violating international law. "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." Armed clashes between Thai and Cambodian forces had broken out at six locations along the disputed border earlier on Thursday, according to military officials, causing civilian casualties, damaging homes and livestock, and prompting the evacuation of residents in Thailand. At least nine people were killed in the violence Thursday, including an 8-year-old boy, the Thai military said. Six people were killed and 10 injured when a Cambodian rocket hit a busy gas station in Kantharalak, Sisaket province, close to the border, the Thai military said. Social media video, geolocated by CNN to Kantharalak, showed several wounded people outside a heavily damaged 7-Eleven convenience store and gas station, with smoke billowing in the background. Thailand also accused Cambodian troops of firing two BM-21 rockets into a civilian area in Kap Choeng district of in Surin province, in Thailand's northeast. Thailand's Ministry of Foreign Affairs said Cambodian attacks on civilian areas continued throughout Thursday, including at a hospital in Surin. Residents of Surin could be seen running for cover and taking shelter in bunkers amid the sound of gunfire, in video from Thai PBS. Thailand's military said it "condemns these violent acts against civilian targets by the Cambodian side and is prepared to take military action to the fullest extent to protect its sovereignty and its people from such inhumane actions." Acting Thai Prime Minister Phumtham Wechayachai earlier said the situation remained delicate and must be addressed with care and with measures in line with international law, according to Reuters news agency. Two hospitals in the province near the site of the clash evacuated patients, according to Thailand's ministry of public health. The clashes came after five Thai soldiers were injured in a landmine explosion on Wednesday, with the incident prompting Thailand to downgrade its diplomatic relations with Cambodia – recalling its ambassador from Phnom Penh and expelling the Cambodian ambassador. Thailand and Cambodia have had a complicated relationship of both cooperation and rivalry in recent decades. The two countries share a 500-mile (800-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. The recent flare-up began early in the morning when Thailand's military said Cambodian troops fired at a Thai army base in an area near the ancient Ta Muen Thom Temple – which lies about 250 miles (400 kilometers) northeast of the Thai capital Bangkok in disputed territory in the south of Thailand's Surin province and in Cambodia's northwest. Thailand said Cambodia had deployed an unmanned drone in front of the temple before sending troops in with weapons. Clashes then erupted along the entire border region with small arms and heavy weapons used, according to Thailand's military. Cambodia has disputed that account. A Cambodian Defense Ministry spokesperson said their troops had acted in self-defense after an unprovoked incursion from Thai soldiers. "Cambodian forces acted strictly within the bounds of self-defense, responding to an unprovoked incursion by Thai troops that violated our territorial integrity," Lieutenant General Maly Socheata said. The country's Defense Ministry accused Thailand of deploying drones, and said Thai forces initiated an armed assault on Cambodian troops stationed at the temple. Cambodia's Prime Minister Hun Manet said in a post on Facebook that Thailand also attacked Cambodian army positions at two temple sites in its Oddar Meanchey province, as well as in Cambodia's Preah Vihear province and Thailand's Ubon Ratchathani province. Hun Manet called on Cambodian citizens to remain calm. The armed clashes come a day after a second Thai soldier in a week lost his leg to a landmine explosion at a different point along the border. Tensions between the two neighbors had already soured in May, when a Cambodian soldier was killed during a clash between Thai and Cambodian troops in which both sides opened fire in a contested border area of the Emerald Triangle, where Cambodia, Thailand and Laos meet. The dispute has since had major political consequences for Thailand and stoked nationalist fervor in both countries. Thailand's Prime Minister Paetongtarn Shinawatra wassuspended from dutiesearlier this month and could face dismissal 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. In 2011, Thai and Cambodian troops clashed in an area surrounding the 11th-century Preah Vihear temple,displacing thousands of peopleon both sides and killing at least 20 people. The ongoing conflict is "likely to get worse before it gets better" and the next few days could see more "confrontation, clashes, escalation," Thitinan Pongsudhirak, a professor of political science at Chulalongkorn University in Bangkok, told CNN. "Each side has so much pent-up tension." This is a developing story and will be updated. For more CNN news and newsletters create an account atCNN.com