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Twin baby elephants have been born this week in a rare event at a national reserve in northern Kenya.

The male and female were first spotted by tour guides out on safari at the Samburu reserve at the weekend.

They are only the second set of twin calves ever to have been encountered by local conservation charity Save the Elephants.

The charity says elephant twins account for only 1% of elephant births, with the last known case recorded in 2006.

Speaking to Reuters news agency, charity founder Dr Iain Douglas-Hamilton said this was a critical time for the calves as the last set of twins born 15 years ago had not survived long after birth.

Quite often the mothers do not have enough milk to feed both calves, he added, saying everyone had their "fingers crossed for their survival".

African elephants have the longest gestation period of any mammal. They carry their young for nearly 22 months, and give birth around every four years.

The ivory trade and loss of vital habitat have led to elephants being put on the International Union for the Conservation of Nature's of endangered species.

However the elephant population has grown in Kenya in recent years, according to the country's first wildlife census, external published last year.