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.