Four of the world's last known remaining eight northern white rhinos have been relocated from captivity back to a Kenyan reserve as part of efforts to save the species from extinction, wildlife authorities said on Monday.

A statement from the Kenya Wildlife Services (KWS) said the animals, two males and two females, arrived at the Ol Pejeta reserve in central Kenya late Sunday after having travelled more than 7,000 kilometres from the Czech zoo that donated them.

Kenyan Forestry and Wildlife Minister Noah Wekesa who received the animals described the subspecies relocation as "a homecoming by one of the rhinos that initially came from Sudan."

He called on the international community help Sudan get any remaining northern white rhinos in its wild for breeding in Kenya.

The weekend successful relocation marked a second attempt by Kenya to introduce new species of rhinos, after the introduction of 70 southern white rhinos whose numbers have grown to a healthy population of 326.

The four were flown from a zoo in the Czech Republic to Kenya, after failing to reproduce since 1985. Two other northern white rhinos remained behind while two others are in San Diego in the U. S..

KWS Head of Species Conservation and Management Patrick Omondi said the aim of the project was to reintroduce the northern white rhinos back to Southern Sudan, Congo and Cameroon.

"That Kenya was chosen for this delicate process is an endorsement of our conservation efforts. Kenya Wildlife Service will strive to ensure that the northern white rhinos are successfully bred and introduced back to their original range. That is our commitment to the world," Omondi said.

Rhino experts believe that releasing the rhinos into their natural habitat in the wild might help them reproduce and survive as a subspecies.

"Northern white rhinos are the world's rarest large mammal," said Rob Brett, Africa Regional Director, Fauna & Flora International and member of the IUCN African Rhino Specialist group.

The rhinos were moved from Dvur Kralové Zoo in the Czech Republic to the Ol Pejeta Conservancy in Laikipia, in central Kenya within the 'Last Chance to Survive' project.

"They are listed as critically endangered on the IUCN Red List of Threatened Species and are thought to be extinct in the wild. Moving them now is a last bid effort to save them and their gene pool from total extinction," he said.

"The Ol Pejeta Conservancy is immensely proud to have received the endorsement of the IUCN African Rhino Specialist Group in hosting these animals, giving them a chance to breed at the 11th hour," said Richard Vigne, Chief Executive Officer, Ol Pejeta Conservancy.

"If we are successful, the preservation of their unique locally adapted genetic traits may allow their natural range to be re- stocked in the coming years."

Conservationists believe that providing the four rhinos with a natural habitat and secure African setting will significantly increase their chances of breeding successfully.

To date, captive breeding of northern white rhino in zoos has had limited success, with breeding only occurring at Dvur Kralove Zoo. The last calf was born in 2000.

The long-term aim of the translocation is to establish a viable breeding group of locally adapted white rhinos for reintroduction back into secure areas of their original range in eastern Africa. The time frame of such a reintroduction could well be in the region of 20 years or more.

"Together with our partners, we plan to provide the remaining individuals with breeding potential their last chance of normal and regular reproduction in a secure location in the wild," said Dana Holeckova, Director of Dvur Kralove Zoo.

"The cause for the move is to induce normal social and territorial behaviour that is essential for the rhinos to breed routinely."

The reintroduction initiative is being carried out by a partnership of conservation organizations, including Fauna & Flora International, the Ol Pejeta Conservancy, Dvur Kralove Zoo, the Lewa Wildlife Conservancy, Back to Africa, and the Kenya Wildlife Service.

The minister said the number of black rhinos in Kenya dropped from 20,000 in 1973 to barely 285 when KWS was formed in 1989. This number has since grown to 609 black rhinos and 326 southern white rhinos that were introduced from South Africa.

Wekesa called on the international community to sustain the ban on trade in ivory and rhino horns.

He faulted Tanzania for coming up with a proposal on the sale of ivory to be discussed in next year's CITES meeting in Doha without consulting its neighbour Kenya, yet it has shared elephant populations in the Masai Mara-Serengeti, Tsavo West-Mkomazi and Amboseli-Kilimanjaro.

"By Tanzania going that route yet we have shared ecosystems, Kenya is likely to lose more rhinos and elephants to poachers," Wekesa said.

Kenya's position on ivory and rhino horn trade has not changed given that it has had to invest so heavily in wildlife protection, including the death of its rangers in the course of duty.

Omondi noted that poaching was on the increase in Africa, with South Africa losing 150 rhinos while Zimbabwe lost 100 rhinos to poachers.

He added that this year alone, Kenya has lost 214 elephants to poachers compared to 47 in 2007, an alarming trend he attributed to the CITES-approved one-off sale experiment of ivory by four southern African countries in 2007.

"Our experience has shown that trade in ivory and rhino horns stimulates illegal killings and that is the basis for Kenya's position on elephant ivory trade at the forthcoming CITES meeting in Doha," he said.