Dangrek Incident

In early 1979, Vietnamese forces overthrew the Democratic Kampuchea regime, and fighting swept toward Khmer Rouge camps on the Cambodia–Thailand border. Facing famine and fear of conscription or retaliation, large numbers of Cambodians sought asylum in Thailand; by the fall of 1979 approximately 140,000 Khmer refugees had crossed, equal to about one percent of Thailand's population. Dega people fleeing the Montagnard resistance also sought passage, but many were caught by Khmer Rouge forces under Son Sen and forced to fight the Vietnamese; mines were planted around detention camps to prevent their escape.

Thailand initially allowed Khmer Rouge combatants to cross for refuge before returning to Cambodia, while blocking civilian refugees "as much as possible." As famine worsened, Thailand laid land mines and closed its borders, leading to refugee encampments on the Cambodian side. UNHCR and researcher Fiona Terry reported pushbacks of refugees in late April and again in May 1979.

On June 5, 1979, Frenchwoman Yvette Pierpaoli traveled to the border and found hundreds of Cambodians detained behind barbed wire, prompting an emergency response effort. According to New York Times correspondent Henry Kamm's June 12 report, Thai officials decided to bus tens of thousands of refugees to the Preah Vihear area of the Dangrek Mountains and force them at gunpoint down a cliff into Cambodia, despite acknowledging the presence of landmines and booby traps. William Shawcross reported that 110 buses arrived at Nong Chan on June 8, 1979, to begin transporting refugees. On June 12, Pierpaoli, U.S. diplomat Lionel Rosenblatt, and two others attempted a rescue at Wat Koh with a list of roughly 25,000 approved-for-resettlement refugees; about 1,500 were saved before Thai officials expelled the group. Most listed refugees were still forced back into Cambodia, and Thai soldiers used physical violence to compel refugees onto buses, confiscating money and property.

Refugees, a majority of them women and children, were forced down a mountainous, forested ridge into minefields; former Lon Nol soldiers were sent first and their bodies helped clear a path. Shawcross reported that a group of refugees who tried to return under a white flag were shot by Thai soldiers after their valuables were taken. Approximately 10,000 refugees remained trapped beneath Preah Vihear for over a week into July, enduring scarce food and water, gunfire directed at those attempting to return, and deaths from disease and exposure.

Death toll estimates vary: Shawcross put the number forced down the cliff at 43,000–45,000; W. Courtland Robinson cited more than 42,000 by June 15. A 1991 Human Rights Watch/Physicians for Human Rights report said thousands died, mostly from dehydration, mines, and diarrhea. Judy Mayotte's 1992 book noted no official death count existed, calling 10,000 dead from shootings and mines alone a "conservative estimate," while UNHCR cited a minimum of 3,000 deaths from shootings, falls, or landmines.

In July, under international pressure, Thailand agreed to readmit 1,000 refugees "who can still be saved." The events prompted a July 23, 1979 Geneva conference on Indochinese refugees and contributed to the later establishment of Thai border refugee camps, including Sa Kaeo and Khao-I-Dang.