Five plantation workers were killed in Cambodia after their vehicle hit an old anti-tank mine in a former Khmer Rouge stronghold, an official said Monday. The driver and two women died instantly in Saturday's blast in the western province of Pailin, said Leng Sochea, deputy secretary general of the Mine Action Authority. Two other people later died in hospital and another eight were injured, he said. The Khmer Rouge regime was toppled in 1979 but civil unrest continued until 1998, and left impoverished Cambodia one of the world's most heavily mined countries along with Afghanistan and Angola. Around 670 square kilometres (258 square miles) still needs to be cleared of explosives, Prime Minister Hun Sen said in February. The number of related casualties dropped to 200 victims a year in 2008-2009, down from 800 annually in the period 2005-6, according to the Cambodian Red Cross. 