The relocation of endangered animals involves putting them to sleep for the journey and then reviving them in a process which carries risks.
According to preliminary investigations by KWS veterinary teams, the deaths resulted from salt poisoning after the animals took water high in salinity when they arrived at their new home.
Rhinos are often moved when their populations outgrow their surroundings.
WWF Kenya also said it supports "launching an urgent independent assessment" to determine why the black rhinos died. "We have to find out what's gone wrong, so that these mistakes are never repeated".
Conservationists have tried to protect the endangered species from poachers targeting the animal for its horn.
A black rhino. Seven have died in unclear circumstances at the Tsavo East National Park.
A KWS spokesman said: "Disciplinary action will definitely be taken if the findings point towards negligence or un-professional conduct on the part of any KWS officers".
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"Moving rhinos is complicated, akin to moving gold bullion, it requires extremely careful planning and security due to the value of these rare animals", she said in a statement. In May, six black rhinos were moved from South Africa to Chad, restoring the species to the country in north-central Africa almost half a century after it was wiped out there.
With a goal of bringing them back, Dean said Kenya aims to increase the number of black rhinos by 2,000.
The eight were among 14 black rhinos, eight from Nairobi National Park and six from Lake Nakuru National Park, which were transported in June in an operation announced by Kenyan Tourism and Wildlife Minister Najib Balala, who has yet to comment on the outcome.
African Parks, a Johannesburg-based conservation group, said earlier this year that there are fewer than 25,000 rhinos in the African wild, of which about 20 percent are black rhinos and the rest white rhinos.
Kenya's black rhino population stands at 750, according to the Worldwide Fund for Nature.
In May, three black rhinos were killed in Kenya's Meru National Park.
The eight dead rhinos were among 11 that had been moved to the sanctuary in an initiative to start a new population in line with the National Rhino Conservation and Management Strategy.
In March, the last male northern white rhino on the planet, an older bull named Sudan, was put down by Kenyan vets after becoming ill.