The United States has struck a deal to reduce Indonesia's debts in exchange for Jakarta pledging about $12 million for programmes to protect endangered species and their habitats on Sumatra island, conservationists said Friday.

The move adds to a similar agreement in 2009, under which the Indonesian government pledged $30 million for increased protection of Sumatra's forests, said NGO Conservation International, which helped broker the deal.

The agreement, which was inked this week, will provide additional funds for environmental groups to improve programmes aimed at protecting the Sumatran low-land rainforests as well as efforts to increase populations of threatened animals.

The forests of Sumatra, a huge island in western Indonesia, are one of the most biodiverse places on the planet and are home to critically endangered Sumatran rhinos and tigers.

"The debt-for-nature swap will benefit critical ecosystems in Sumatra through increasing conservation efforts," Conservation International said in a statement.

"The United States is proud to partner with the government of Indonesia and the NGO sector to help protect and preserve the diverse wildlife that exists on Sumatra," said Kristen Bauer, charge d'affaires at the US embassy in Jakarta.

Under the agreement, the Indonesian government will pay about $12 million over seven years into a trust that will issue grants for the conservation efforts, Conservation International said.

The US government contributed most of the money for the debt swap, while Conservation International also gave some.