When Lon Nol assumed power in 1970, the Khmer Republic government launched a propaganda campaign to portray the ethnic Vietnamese as agents of the Vietcong. About 30,000 Vietnamese were arrested and killed in prison, while an additional tens of thousands fled to Vietnam. Five years later in 1975, less than 80,000 Vietnamese remained in Cambodia when the Khmer Rouge seized power. Close to three quarters of them were expelled to Vietnam, and the remaining 20,000 who remained are those who are of mixed-Vietnamese and Khmer descent. Those who remained were killed by the regime. By the time Vietnamese troops entered Cambodia in 1979, virtually all of Cambodia's Vietnamese population were either displaced or killed. Vietnam established a new regime known as the People's Republic of Kampuchea (PRK), and Vietnamese advisers were appointed in the new government administration. In 1983, the PRK government formulated an official policy to encourage former Vietnamese residents of Cambodia to return and settle down. Vietnamese immigrants who had no family ties to Cambodia also came to settle in the country, as there was little border control to limit Vietnamese migrants from entering the country. The Vietnamese were recognised as an official minority under the PRK regime, and Overseas Vietnamese Associations were established in parts of Cambodia with sizeable Vietnamese populations. The PRK government also identity cards were issued to them until the withdrawal of Vietnamese troops in 1990.