Estimates as to how many people were killed by the Khmer Rouge regime range from approximately one to three million; the most commonly cited figure is two million (about a quarter of the population). This era gave rise to the term Killing Fields, and the prison Tuol Sleng became notorious for its history of mass killing. Hundreds of thousands fled across the border into neighbouring Thailand. The regime disproportionately targeted ethnic minority groups. The Cham Muslims suffered serious purges with as much as half of their population exterminated. Pol Pot was determined to keep his power and disenfranchise any enemies or potential threats, and thus increased his violent and aggressive actions against his people.