Thailand and Cambodiaexchanged fire along their disputed border fora second dayon Friday, officials from both countries said, with more than a dozen people reported killed and more than 100,000 civilians evacuated. Tensions between the Southeast Asian neighbors have been boiling for months over disputed sections of their 500-mile (800-kilometer) land border, demarcated partly by Cambodia's former colonial ruler France, and which runs near several archaeologically significant religious sites that both countries claim. Clashes broke out at 4:30 a.m. local time on Friday after Cambodia initiated firing, using small arms and heavy weapons, Col. Richa Sooksuwanon, the deputy spokesperson for the Thai army, told CNN. The Thai army responded with artillery fire, he said. Clashes were taking place in two locations in Ubon Ratchathani province and one in Surin province, the Thai Army said, warning the public to avoid the area. Heavy weapon and rocket fire had been reported coming from Cambodia, it said. It also warned that its forces were conducting bomb disposal operations and recovering bodies from the Kantharalak district that had been hit by Cambodian rockets on Thursday. Videos shared by Reuters news agency on Friday showed Thai artillery firing, each shot emitting loud booms and smoke into the air. Thursday's clashes saw exchanges of small arms and rocket fire between Thailand – a United States treaty ally – and its smaller neighbor Cambodia. Thailand later scrambled F-16 jets and bombed what it said were military targets inside Cambodia. Both countries also have close ties with China, which, along with the US, has called for de-escalation. An undated video shared by the Thai army showed drones dropping bombs on what it said were several military targets inside Cambodia. Smoke and flames erupted after the sites – which appear to be in forested areas – were hit. CNN has not been able to verify the video. At least 14 people have beenkilledso far in Thailand, mostly civilians, according to Thailand's Ministry of Public Health. And in Cambodia, at least one person has been killed and five wounded, according to Met Measpheakdey, a spokesperson from Oddar Meanchey province, which borders Thailand's Buri Ram, Surin and Si Saket provinces. He added that as of Friday morning, tensions were "still heated." "The exchange of fighting… is still happening," he said. Cambodian officials accused the Thai military of using cluster munitions at two locations early Friday. CNN has contacted the Thai military for comment. More than 4,000 people in Cambodia have been displaced from their homes near the border, the Associated Press reported on Friday, citing another official from Oddar Meanchey. Videos from Oddar Meanchey on Thursday showed villagers fleeing in the dead of night, packing their belongings into vehicles and sleeping under tarps. As of Thursday night, more than 100,000 Thai residents had evacuated to temporary shelters, according to the Ministry of Interior. Footage from Surin province showed evacuees sheltering in a university, resting on mats on the floor and eating out of plastic containers. In a different part of the province, evacuee Ngerntra Pranoram said she was "shocked" by the fighting. "Nobody wants this to happen. I feel for the elderly and the disabled. It's very difficult for them to get here," she said, according to Reuters. "Some people have cars, which is good, but for those who don't, it's really hard." The recent flare-up came after five Thai soldiers were wounded in a landmine explosion on Wednesday. But tensions had been building since May, when a Cambodian soldier was killed during a clash between Thai and Cambodian troops in which both sides opened fire in another contested border area of the Emerald Triangle, where Cambodia, Thailand and Laos meet. Thailand and Cambodia have a relationship of both cooperation and rivalry. They share a 500-mile (800-kilometer) land border — largely mapped by France when it ruled Cambodia — that has periodically seen military clashes and been thesource of political tensions. "Both sides, Cambodians and Thais, feel resentful of history," said Thitinan Pongsudhirak, a professor of political science at Chulalongkorn University in Bangkok. "Thais think that the French took some land from Thailand, gave it to Cambodia. Cambodians think that this is their civilization from a long, long time ago, and ultimately this is their land." But it's not an evenly matched fight. Thailand's military dwarfs Cambodia's in both personnel and weaponry; its 361,000 active-duty personnel is three times Cambodia's manpower. And the United States classes Thailand as a major non-NATO ally, enabling Bangkok to enjoy decades of US support for its weapons programs. Thailand is currently wracked with uncertainty; its Prime Minister Paetongtarn Shinawatrasuspended 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. Thailand's military has long been a major player within the kingdom's politics and has seized power in multiple coups, often toppling democratic governments. It portrays itself as the ultimate defender of the monarchy. CNN's Patrick Sarnsamak and Len Leng contributed reporting. For more CNN news and newsletters create an account atCNN.com