These developments, magnified by Sihanouk's abiding suspicions, eventually undermined Phnom Penh's relations with Washington. In November 1963, the prince charged that the United States was continuing to support the subversive activities of the Khmer Serei in Thailand and in South Vietnam, and he announced the immediate termination of Washington's aid program to Cambodia. Relations continued to deteriorate, and the final break came in May 1965 amid increasing indications of airspace violations by South Vietnamese and by United States aircraft and of ground fighting between Army of the Republic of Vietnam (ARVN) troops and Viet Cong insurgents in the Cambodian border areas.