By Agence France-Presse
The premier -- one of the world's longest serving leaders -- is seeking to prolong his 33-year grip on power in the national vote set for July 29 and has used the courts to cripple his opponents.
But he has also tried to cultivate a lighter side.
"Today we are all happy to inaugurate the animal zoo, the Phnom Penh Safari," Hun Sen said in a speech to thousands at the park before a ribbon-cutting ceremony, adding that the site of the sprawling complex was a former ammunition depot for remnants of the brutal Khmer Rouge regime.
The $9 million safari will house 89 types of animals, including bears, ostriches, kangaroos, giraffes, tigers and deer.
The zoo is run by a company owned by tycoon Ly Yong Phat, a senator from the ruling Cambodian People's Party.
After the official unveiling Hun Sen took a tour of the grounds and sat down to watch the orangutan show, a common form of entertainment at Southeast Asian zoos that animal rights activists have long been critical of.
The 65-year-old strongman smiled as the apes performed a variety of slapstick routines, including gyrating to music.
In the kickboxing event they drubbed one another over the head and delivered a series of punches, knees and kicks, while a presenter narrated the fight.
Afterwards Hun Sen congratulated one of the fighters by holding up the orangutan's arm as bodyguards loomed nearby.
The day was not entirely devoid of politics as Hun Sen used his opening remarks to ask people to vote for his party.
Yet Hun Sen will face little competition at the polls.
The country's main opposition party was dissolved under a court order last year as part of the sweeping crackdown of dissent, and western democracies have withdrawn support for the vote.
Former opposition lawmakers -- mostly those who fled the country in the wake of the crackdown -- have also urged voters to boycott July's poll in protest.