fall of Saigon, congratulating them on the seventh anniversary of their establishment. In July 1976, following the establishment of the Socialist Republic of Vietnam as a reunified country, Phnom Penh Radio broadcast a commentary which proclaimed the "militant solidarity and friendship between peoples of Democratic Kampuchea and the Socialist Republic of Vietnam grow constantly greener and sturdier". However, during that same month, Pol Pot publicly hinted at tensions between Vietnam and Kampuchea when he told a visiting Vietnamese media delegation that there were "obstacles and difficulties" in the relationship between the two countries. Nonetheless, on 21 September 1976, the first air service connecting Hanoi and Ho Chi Minh City with Phnom Penh was established. Then in December 1976, the Kampuchean Revolutionary Organisation sent greetings to the Vietnamese Communist Party during their Fourth Congress. 1977: incursions and build-up to war Towards the end of 1976, while Vietnam and Kampuchea publicly appeared to be improving their relationships, the private suspicions of both countries' leadership grew. From the Vietnamese perspective, they were the patrons of genuine Marxist–Leninist revolutions in Southeast Asia, so it was vital for them to exercise control over the Kampucheans and the Laotians. Indeed, that was the reason North Vietnam supported the Khmer Rouge during their fight against the Lon Nol government, in the hope that the Kampuchean communists would adopt a pro-Vietnamese line upon their victory in the same way as the Pathet Lao had done. However, their hopes were dashed as early as 1973, because People's Army of Vietnam (PAVN) formations operating in Khmer Rouge-occupied territories were occasionally subjected to armed attacks by their allies. The Vietnamese position inside Kampuchea was further weakened after the end of the war, as there were no pro-Vietnamese elements left within the Kampuchean Communist Party. When the pro-Chinese Pol Pot and his brother-in-law Ieng Sary resigned from their respective positions as premier and foreign minister in September 1976, Vietnamese Prime Minister Phạm Văn Đồng and General Secretary of the Communist Party Lê Duẩn were optimistic that Vietnam could exercise greater influence on the Kampucheans. In a private meeting with the Soviet ambassador to Vietnam on 16 November 1976, Lê Duẩn dismissed both Ieng Sary and Pol Pot as "bad people" for their pro-Chinese policies. Le Duan then asserted that Nuon Chea, who had ascended to the position of Premier of Democratic Kampuchea as Pol Pot's replacement, was a person of pro-Vietnamese orientation,