The fatwa by the Indonesian Ulema Council declares such activities "unethical, immoral and sinful", council official Asrorun Ni'am Sholeh told AFP.
"All activities resulting in wildlife extinction without justifiable religious grounds or legal provisions are haram (forbidden). These include illegal hunting and trading of endangered animals," said Sholeh, secretary of the council's commission on fatwas.
"Whoever takes away a life, kills a generation. This is not restricted to humans, but also includes God's other living creatures, especially if they die in vain."
However, a Forestry Ministry official who asked to remain anonymous told AFP the ministry and the religious council would make a joint announcement regarding the fatwa on March 12, without elaborating on its content.
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The WWF called the fatwa the first of its kind in the world, and said the use of religion for wildlife protection "is a positive step forward."
"It provides a spiritual aspect and raises moral awareness which will help us in our work to protect and save the remaining wildlife in the country such as the critically endangered tigers and rhinos," WWF Indonesia communications director Nyoman Iswara Yoga said.
Acknowledging it was not legally binding, Sholeh said in English "It's a divine binding."
He said the fatwa was effective from January 22. It was only made public late yesterday.