The Khmer Rouge attempted invasions to recover the territory which, in part, led to Vietnam's invasion of Cambodia and deposition of the Khmer Rouge. In 1955, Sihanouk abdicated in favour of his father to participate in politics and was elected prime minister. Upon his father's death in 1960, Sihanouk again became head of state, taking the title of prince. As the Vietnam War progressed, Sihanouk adopted an official policy of neutrality in the Cold War. Sihanouk allowed the Vietnamese communists to use Cambodia as a sanctuary and a supply route for their arms and other aid to their armed forces fighting in South Vietnam. This policy was perceived as humiliating by many Cambodians. In December 1967 Washington Post journalist Stanley Karnow was told by Sihanouk that if the US wanted to bomb the Vietnamese communist sanctuaries, he would not object unless Cambodians were killed. The same message was conveyed to US President Johnson's emissary Chester Bowles in January 1968. However, in public Sihanouk refuted the right of the U.S. to use air strikes in Cambodia, and on 26 March he said "these criminal attacks must immediately and definitively stop". On 28 March a press conference was held and Sihanouk appealed to the international media: "I appeal to you to publicise abroad this very clear stand of Cambodia—that is, I will, in any case, oppose all bombings on Cambodian territory under whatever pretext." Nevertheless, the public pleas of Sihanouk were ignored and the bombing continued. Members of the government and army became resentful of Sihanouk's ruling style as well as his tilt away from the United States. Khmer Republic (1970–75) While visiting Beijing in 1970 Sihanouk was ousted by a military coup led by Prime Minister General Lon Nol and Prince Sisowath Sirik Matak. US support for the coup remains unproven. However, once the coup was completed, the new regime, which immediately demanded that the Vietnamese communists leave Cambodia, gained the political support of the United States. The North Vietnamese and Viet Cong forces, desperate to retain their sanctuaries and supply lines from North Vietnam, immediately launched armed attacks on the new government. The king urged his followers to help in overthrowing this government, hastening the onset of civil war. Soon Khmer Rouge rebels began using him to gain support. However, from 1970 until early 1972, the Cambodian conflict was largely one between the government and army of Cambodia, and the