GENEVA: Sumatra's endangered elephants and tigers should get a boost from an Indonesian government move to expand one of their last havens, a four-year-old national park on the island, conservation body WWF said on Thursday.

But WWF warned that increased efforts would be vital to ensure that poaching and other illegal activities -- like unsanctioned logging and settlement -- did not continue in the park, Tesso Nilo in Sumatra's Riau Province.

"This is an important milestone towards securing a future for the Sumatran elephant and tiger," said Mubariq Ahmad, head of WWF in Indonesia as it was announced in Jakarta that the park area would be more than doubled to 86,000 hectares (212,500 acres).

"Tesso Nilo is still under serious threat from illegal activities, but if we can protect the forests there it will give some of Sumatra's most endangered wildlife the breathing room they need to survive," declared Ahmad.

WWF, whose international headquarters are at Gland near Geneva, said 60 to 80 elephants and some 50 tigers were believed to live in the area now to be covered by the park.

Set up in 2004 with 38,000 hectares (93,900 acres), it also has the highest lowland forest plant diversity known to science. Some 4,000 unique species have been recorded and many more remain to be discovered, WWF said.

Riau Province is home to about 210 elephants, down from around 1,250 just 25 years ago, and 192 tigers, whose numbers have dropped from around 650 over the same period.

The main cause of the decline of both Sumatran species, WWF indicated, is deforestation, the rate of which in Riau is the highest of any Indonesian province.

Some 65 percent of Riau's forest cover, key to the animals' survival, has disappeared since the early 1980s, largely as a result of increased activity by global pulp and palm oil companies -- and from illegal logging.

WWF said two of the world's largest pulp and paper mills are located in the province, which had lost more natural forest to pulpwood concessions than any other in Indonesia.

The clearing of carbon-rich peat land and peat forests in Riau have contributed to Indonesia having the world's third highest rate of greenhouse gas emissions, behind only the United States and China, the conservation body added.