Thirteen Patas monkeys have died after fire sparked by a faulty generator swept through their enclosure in the drive-through attraction at Woburn Safari Park.
The overnight blaze at the Bedfordshire park's African Forest appears to have centred on the Patas Monkey house with other nearby animals apparently unaffected.
Three crews from Bedfordshire Fire Brigade attended and extinguished the fire before later confirming the cause.
"Following our fire investigation at Woburn Safari Park we have concluded that it is likely that the fire started accidentally in a generator," a spokesperson said.
The park remained open though the jungle enclosure was closed to visitors.
Firefighters were called to the scene shortly after 2.30am on Tuesday when the fire was spotted by security guards on a routine patrol.
But fire station commander Paul Goddard said he believed all the monkeys had died before crews arrived at the scene.
"They found the outbuilding housing Patas monkeys was well alight and its roof had fallen in," a spokesman for the service said.
"They fought the fire using fire hoses while wearing breathing apparatus to protect themselves from the smoke and fumes. The building was 90% damaged by the fire."
A statement from Woburn said: "Staff and fire crews attended the scene, however devastatingly for everyone at the park, none of the 13 (monkeys) could be saved.
"All other animals within the jungle drive-through enclosure are being monitored, but early signs suggest that they have not been affected.
"An investigation is under way into the cause of the fire and whilst the park will remain open, the Jungle enclosure will remain closed for investigation.
"The park is grateful to the quick response from Bedfordshire Fire Brigade, who attended with three appliances."
The blaze wiped out all of the park's Patas monkey troop, and, according to website UK Zoos, the only other place in the UK that houses them is Colchester Zoo in Essex.
It is the second fire to strike animal centres in less than two weeks, after one that struck at London Zoo on December 23, killing an aardvark and four meerkats.
What distinguishes Patas monkeys?
The ground-dwelling Patas monkey is the world's fastest primate, capable of speeds of up to 34mph, and known for its distinctive warning calls in response to predators.
The animals originate from West and East Africa and live in open savanna rather than dense woodlands.
The monkeys at Woburn could roam a 16 acre exhibit but were housed at night during the winter.
The 13 monkeys were part of the road safari in the African Jungle along with Barbary macaques and herd of Eastern Mountain Bongo.