A land mine left over from Cambodia's three decades of civil war has killed six farmers who were returning from planting rice, a mine clearance official said Thursday, according to AP. The men had been riding a homemade tractor Wednesday in the northern province of Preah Vihear when the anti-tank mine exploded, said Heng Ratana of the Cambodian Mine Action Center, a government agency that oversees mine clearing. He said a seventh man was critically injured. The accident underlined the danger posed by the estimated 4 million to 6 million uncleared land mines and other pieces of unexploded ordnance that kill or maim more than 200 people each year. There have been more than 60,000 casualties since 1979, when the Khmer Rouge were ousted from power and began their long-running insurgency.