Prime Minister Hun Manet signed the order in January leasing a 99-hectare (245-acre) plot of land inside the Prey Lang Wildlife Sanctuary to KP Cement "for investment in a plan to set up a cement factory", the document said.

KP Cement is a politically connected company already operating mining pits for limestone and marble in Prey Lang, according to US-based conservation news website Mongabay, which first reported the approval.

It published satellite imagery it said showed forest clearance in the concession.

Limestone is a key ingredient in cement, which is in high demand to feed Cambodia's construction boom, and has been linked to environmental degradation in the country.

Prey Lang straddles four provinces in central Cambodia and was targeted by successive mining operations before the government in 2023 declared a moratorium on new mining licenses in the protected forest.

Government officials could not be reached immediately for comment on the licence or its implications for the moratorium.

At 489,663 hectares, Prey Lang is the largest remaining lowland evergreen forest in mainland Southeast Asia, according to Conservation International, which has worked in the area since 2005.

It is also Cambodia's largest protected area, though it has some of the highest rates of deforestation in the country, according to the group.

Heng Kimhong, an environmental and human rights activist, urged the government to conduct a thorough environmental impact assessment for the project.

"I worry that it will impact the biodiversity in the area," he told AFP, adding he has not seen any environmental impact assessment on the project yet.

Unchecked illicit logging has contributed to a sharp drop in Cambodia's forest cover over the years, according to activists.

From 2002 to 2023, a third of Cambodia's humid primary forests -- some of the world's most biodiverse and a key carbon sink -- were lost, according to monitoring site Global Forest Watch.