The USA ensures that the Khmer Rouge keeps Cambodia's seat at the United Nations even though it is longer in power. This is partially for revenge on Vietnam (who defeated the USA militarily), and partially to please the USA's new ally China (who are the principal supporters of the Khmer Rouge and are opposed to Vietnam).
The USA turns a blind eye as China supplies the Khmer Rouge with arms via Thailand. In 1981, Zbigniew Brzezinski, the USA president's security adviser would admit:
"I encouraged the Chinese to support Pol Pot."
The USA and Thailand supplied the Khmer Rouge under the cover of humanitarian aid. Two USA relief aid workers, Linda Mason and Roger Brown, later wrote:
"The US Government insisted that the Khmer Rouge be fed ... the US preferred that the Khmer Rouge operation benefit from the credibility of an internationally known relief operation."
