Three Thai soldiers were killed on Tuesday during a landmine clearance mission near the Thai- Cambodian border, media reported. The incident occurred Tuesday afternoon when a seven-soldier patrol was assigned to clear anti-tank landmines in Klonghad district in Thailand\'s northeastern province of Sa Kaew, Thai News Agency reported. As a landmine went off suddenly, three of them were killed on spot.Another soldier was critically injured and rushed to a local hospital. The cause of the incident is still under investigation and the area is off-limits to the public for safety reasons.The landmines were planted in the 1970s and 1980s during the decades of chronic conflicts in Cambodia.