IUCN, the International Union for Conservation of Nature, raised its listing of the Sumatran elephant subspecies from "endangered" to "critically endangered" after nearly 70 percent of its habitat and halve its population has been lost in one generation.

The main culprit is deforestation of habitat or its conversion to use for agriculture, a practice that has also raised the specter of extinction for the Sumatran tiger and the Javan rhino.

"The Sumatran elephant joins a growing list of Indonesian species that are critically endangered, including the Sumatran orangutan, the Javan and Sumatran rhinos and the Sumatran tiger," said Carlos Drews, Director of WWF's Global Species Programme, in a statement.

"Unless urgent and effecting conservation action is taken these magnificent animals are likely to go extinct within our lifetime."

There are only an estimated 2,400 to 2,800 elephants of the Sumatran subspecies alive in the wild, down about 50 percent from a 1985 estimate. Scientists say that if current trends continue, the animals could be extinct in the wild in less than 30 years, WWF said.

The organization called on the Indonesian government to prohibit all forest conversion in elephant habitats until a conservation strategy is devised.

Although Sumatran elephants are protected under Indonesian law, a vast majority of their habitats are outside protected areas and could be converted to agricultural use, IUCN was quoted as saying.

The situation is particularly critical in central Sumatra's Riau Province, where rapid deforestation has cut elephant numbers by 80 percent in less than 25 years, WWF added.

"Riau Province has already lost six of its nine herds to extinction," said Anwar Puroto of WWF-Indonesia.

"Forest concession holders such as pulp and paper companies and the palm oil industry have a legal and ethical obligation to protect endangered species within their concessions."

Last May, a two-year moratorium on new permits to clear primary forests came into effect in Indonesia, part of a $1 billion deal with Norway that could spur projects to cut emissions and slow expansion of plantations. But the long-delayed moratorium was breached on its first day, an environmental group said.

In the last 70 years, Indonesia has lost both the Bali tiger and the Java tiger.

(Reporting by Elaine Lies; editing by Jonathan Thatcher)

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