On 8 January 1979 the pro-Vietnamese People's Republic of Kampuchea (PRK) was established in Phnom Penh, marking the beginning of a ten-year Vietnamese occupation. During that period, the Khmer Rouge's Democratic Kampuchea continued to be recognised by the United Nations as the legitimate government of Kampuchea, as several armed resistance groups were formed to fight the Vietnamese occupation. Throughout the conflict, these groups received training in Thailand from the British Army's Special Air Service. Behind the scenes, Prime Minister Hun Sen of the PRK government approached factions of the Coalition Government of Democratic Kampuchea (CGDK) to begin peace talks. Under diplomatic and economic pressure from the international community, the Vietnamese government implemented a series of economic and foreign policy reforms, and withdrew from Kampuchea in September 1989.