LOS ANGELES — Africa’s Western black rhino has officially been declared extinct and other subspecies of rhinoceros could follow, according to the latest review by a leading conservation organization.

The International Union for Conservation of Nature listed the Northern white rhino in central Africa as “possibly extinct in the wild” and the Javan rhino as “probably extinct” in Vietnam.

The organization blamed a lack of political support for conservation efforts in many rhino habitats, international organized crime groups targeting the animal, increasing illegal demand for rhino horns and commercial poaching.

“In the case of both the Western black rhino and the Northern white rhino, the situation could have had very different results if the suggested conservation measures had been implemented,” Simon Stuart, chairman of IUCN’s Species Survival Commission, said in a statement Thursday. “These measures must be strengthened now, specifically managing habitats in order to improve breeding performance, preventing other rhinos from fading into extinction.”

The last Javan rhino in Vietnam is believed to have been killed by poachers in 2010, reducing the species to a tiny, declining population in Java.

The rhinos were among more than 61,900 animal and plant species reviewed for the IUCN’s latest Red List of Threatened Species. A quarter of the mammals on the Red List were found at risk of extinction. But the organization said there have also been conservation successes.

Fewer than 100 southern white rhinos survived at the end of the 19th century, but the population in the wild is now believed to number over 20,000.