Industrial activity such as mining and logging threatens almost half of the world's natural World Heritage sites, from Australia's Great Barrier Reef to the Inca citadel of Machu Picchu in Peru, the World Wide Fund for Nature, or WWF, said in a report on Wednesday.

It urged companies to obey UN appeals to declare all heritage sites "no go" areas for oil and gas exploration, mines, unsustainable timber production and overfishing.

A total of 114 World Heritage sites out of 229 worldwide that are prized for nature or a mixture of nature and culture were under threat, the WWF study said.