LONDON (AFP) - Angolas capital Luanda retained the unenviable title of the worlds most expensive city for expatriates, narrowly edging out Tokyo, according to a survey published Tuesday. At the other end of the scale, the Mercer groups study named the Pakistani port Karachi as the least expensive city, with living around three times cheaper than in Luanda. Oil-rich Angola is a magnet for foreign workers who push up already high prices inflated by a reliance on imports. The southern African nations domestic production lags behind its neighbours due to the effects of a 27-year-long civil war on its infrastructure. Another African city, the Chadian capital NDjamena, was placed third with Moscow fourth and Geneva fifth. Paris dropped 10 places to 27th while London dropped one place to 18th. New York at 32nd was named as the most expensive metropolis in the United States.