Three foreign tourists were killed on Friday during an adventure tour at Datanla waterfall in Vietnam's Lam Dong province.According to authorities, the victims were one man and two women -- all British, Xinhua news agency reported.The bodies were found from an abyss in the downstream area of the waterfall.The driver of a local travel firm booked by the tourists said he drove them to the site at 11.30 a.m.Police said the victims might have slipped into the waterfall when exploring the area.