Former US President Richard Nixon was baffled and annoyed by Americans' sympathies for India, which he described as a "physiological disorder", says a new book based on declassified documents.

He scorned a "phobia" among some Americans that "everything India does is good, and everything Pakistan does is bad", and once told the military leader of Pakistan (Yahya Khan), "There is a psychosis in this country about India," writes Princeton University professor Gary J Bass in "The Blood Telegram: India's Secret War in East Pakistan."

The book, published by Random House India, is a riveting history of the Pakistani army's crackdown on the then East Pakistan (today's independent Bangladesh), killing thousands of people and sending 10 million refugees fleeing into India.