According to the CPK's own figures, by August 1977 between 4000 and 5000 party members had been liquidated as "enemy agents" or "bad elements". In 1978, the government initiated a second purge, during which tens of thousands of Cambodians were accused of being Vietnamese sympathisers and killed. At this point the remaining CPK members who had spent time in Hanoi were killed, along with their children. In January 1978, Pol Pot announced to his colleagues that their slogan should be "Purify the Party! Purify the army! Purify the cadres!" Foreign relations Outwardly, relations between Cambodia and Vietnam were warm following the establishment of Democratic Kampuchea; after Vietnam was unified in July 1976, the Cambodian government issued a message of congratulations. Privately, relations between the two were declining. In a speech on the first anniversary of their victory in the civil war, Khieu referred to the Vietnamese as imperialists. In May 1976, a negotiation to draw up a formal border between the two countries failed. On taking power, the Khmer Rouge spurned both the Western states and the Soviet Union as sources of support. Instead, China became Cambodia's main international partner. With Vietnam increasingly siding with the Soviet Union over China, the Chinese saw Pol Pot's government as a bulwark against Vietnamese influence in Indochina. Mao pledged $1 billion in military and economic aid to Cambodia, including an immediate $20 million grant. Many thousands of Chinese military advisors and technicians were also sent to the country to assist in projects like the construction of the Kampong Chhnang military airport. The relationship between the Chinese and Cambodian governments was nevertheless marred by mutual suspicion and China had little influence on Pol Pot's domestic policies. It had greater influence on Cambodia's foreign policy, successfully pushing the country to pursue rapprochement with Thailand and open communication with the U.S. to combat Vietnamese influence in the region. After Mao died in September 1976, Pol Pot praised him and Cambodia declared an official period of mourning. In November 1976, Pol Pot travelled secretly to Beijing, seeking to retain his country's alliance with China after the Gang of Four were arrested. From Beijing, he was then taken on a tour of China, visiting sites associated with Mao and the Chinese Communist Party. The Chinese were the only country allowed to retain their old Phnom Penh embassy. All other diplomats were made to live in assigned quarters on