few heavy tanks, 200 armoured vehicles and limited air capability. Despite facing such heavy odds, Kampuchea showed no signs of hesitation as its military continued to assault Vietnam's border regions. In January 1978, KRA forces still held portions of Vietnamese territory and began overrunning Vietnamese outposts in Hà Tiên Province. On 27 January 1978, Vietnam started calling on the KRA along the border regions to overthrow the Khmer Rouge government. Against the backdrop of military clashes, between 9 January and 20 February 1978, Vietnamese Deputy Foreign Minister Phan Hien made several trips to Beijing to hold discussions with representatives of the Kampuchean government, which ultimately proved to be fruitless. On 18 January 1978, China attempted to mediate between Kampuchea and Vietnam when Vice Premier Deng Yingchao (widow of Zhou Enlai) travelled to Phnom Penh, where her effort was met with strong resistance by Kampuchean leaders. Meanwhile, Vietnamese government officials began conducting secret meetings with So Phim, the Khmer Rouge leader in Kampuchea's Eastern Military Zone, to plan a military uprising backed by Vietnam. During that same period, military setbacks experienced by the KRA in the Eastern Military Zone prompted Pol Pot to label the region as a "nest of traitors". In order to purge the Eastern Military Zone of those he perceived to have been contaminated by the Vietnamese, Pol Pot ordered military units from the Southwest Zone to move into eastern Kampuchea and eliminate the "hidden traitors". Unable to withstand an attack from the Kampuchea Government, So Phim committed suicide while his deputy Heng Samrin defected to Vietnam. On 12 April 1978, the Kampuchean government declared they and Vietnam could negotiate again if the Vietnamese gave up their expansionist ambitions and recognised Kampuchea's sovereignty. However, there was also a pre-condition requiring Vietnam to meet several obligations through a seven-month trial ceasefire. The Vietnamese government immediately rejected the demand. In response, two KRA divisions penetrated up to into Vietnamese territory and massacred over 3,000 Vietnamese civilians in the village of Ba Chúc in An Giang Province. In June 1978, the VPAF started bombing KRA positions along the border regions, flying about 30 bombing sorties per day and inflicting heavy casualties on the Kampucheans. By that stage in the conflict, most surviving leaders of the Eastern Military Zone had escaped into Vietnam, where they assembled at various secret camps with the purpose of forming a Vietnamese-backed "liberation army" to fight against