Twin Amur leopards, the world's most endangered big cat species, born at San Diego Zoo

The San Diego Zoo on Tuesday announced the birth of twin Amur leopard cubs, the world's most endangered species of big cat.

According to a Facebook post, the twins' mother,  Satka, gave birth to the cubs – the third set of Amur leopard twins to be born at the zoo.

"Satka is fur-miliar with her motherly duties," the post reads. "When she's not in the den grooming and nursing the cubs, she is keeping a watchful eye as they begin to explore the habitat outside."

The zoo did not say whether the cubs have been named.

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An endangered species

Their births increase the cat’s slim estimated population. Amur leopards are thought to be the world’s rarest big cat, with only about 120 left in the wild in Russia and China, according to the World Wildlife Fund.

The animals have thick, luscious, black-ringed coats and a huge furry tails they can wrap around themselves to keep warm.

The Amur leopard is nocturnal and lives and hunts alone, mainly in the forests of Russia and China.

During winter, the hairs of that unique coat can grow as long as 3 inches.

Natalie Neysa Alund covers breaking and trending news for USA TODAY. Reach her at nalund@usatoday.com and follow her on Twitter @nataliealund.

This article originally appeared on USA TODAY: Amur leopards born at San Diego Zoo; species critically endangered