Along with
Heng Samrin,
Chea Sim, and
Hun Sen, Sar Kheng was among the Democratic Kampuchea cadres of the Eastern Zone.
[6] However, after commander of the Eastern Zone Sar Phim
[7] was assassinated, Sar Kheng,
Hun Sen, and other leaders who refused the purges of the
Cambodian genocide went into the opposition against the Khmers Rouges.
[8] The ties and friendships made at that time have lasted and still continue to determine Cambodian politics.
Since they fled to Vietnam, they have been accused of being pro-Vietnamese. After the Vietnamese troops entered Cambodia and pushed back the Khmers Rouge to the North West provinces, Kheng, along with his brother-in-law Chea Sim, took on leadership positions in national security and were identified as "hard-liners" in the People's Republic of Kampuchea government, fighting to eradicate the Khmer Rouge from Cambodia.[9]