Professor Prithvi Nath Dhar, an eminent economist who served as Principal Secretary to Prime Minister Indira Gandhi in the 1970s, died here today. He was 94 and died of age-related problems. A professor of Economics in Delhi University for many years, Dhar was one of the founders of the Delhi School of Economics.He served as the United Nations Assistant Secretary General, Research and Policy Analysis, in New York from 1976 to 1978. Dhar, who was the only person in the Prime Minister's Office those days who was not from either the IAS or the IFS, had joined the PMO in 1970.Prime Minister Dr. Manmohan Singh has condoled his death.