According to the report, Cambodia is on the verge of again becoming a one-party state and is calling on countries, including Australia, to impose travel bans on the personnel who've been the "backbone" of Hun Sen's political regime.
"Hun Sen really has become a fully-fledged military dictator, a fact that he hopes to hide behind the fig-leaf of a national election in July that will be neither free nor fair," Human Rights Asia deputy director Phil Robertson said.
Human Rights Watch says the regime has been driving a massive crackdown ahead of next month's national elections.
Cambodian-Australian community to go ahead with protests against Cambodia's PM
Over the past 12 months, the Cambodia National Rescue Party (CNRP) has been dissolved, the official leader of the party, Kem Sokha, jailed on treason charges and the founding leader of the party, Sam Rainsy has been forced into exile after he was convicted of what Human Rights Watch calls trumped-up charges.
The report also highlights the media crackdown in Cambodia where journalists have been arbitrarily detained, newspapers forced to close and radio stations ordered not to broadcast news from foreign media such as Radio Free Asia and Voice of America.
Human Rights Watch believes the regime is cracking down because it fears Cambodia's urban and younger voters are more likely to support the opposition in next month's national elections.