Indigenous people must give prior consent for any economic activity on their ancestral lands, Pope Francis insisted Wednesday as the U.S. administration of Donald Trump seeks to advance construction on the $3.8-billion Dakota Access pipeline.

Francis, who met with representatives of Indigenous people attending a UN agricultural meeting, said the key issue facing them is how to reconcile the right to development with protection of their cultures and territories.

"In this regard, the right to prior and informed consent should always prevail," he said. "Only then is it possible to guarantee peaceful co-operation between governing authorities and Indigenous peoples, overcoming confrontation and conflict."

Indigenous groups oppose pipeline

The Cheyenne River and Standing Rock Sioux reservations are suing to stop construction on the final stretch of the Dakota Access pipeline, which would bring oil from North Dakota's rich Bakken fields across four states to a shipping point in Illinois.

They say the pipeline, being built by Texas-based Energy Transfer Partners, threatens their drinking water, cultural sites and ability to practice their religion, which depends on pure water. The last piece of the pipeline is to pass under a reservoir on the Missouri River, which marks the eastern border of both tribes' reservations.

Energy Transfer Partners has insisted the water supply will be safe.

Francis didn't cite the Dakota pipeline dispute by name and the Vatican press office said he was not making a direct reference to it. But history's first Latin American Pope has been a consistent backer of Indigenous rights and has frequently spoken out about the plight of Indigenous people in resisting economic development that threatens their lands.

"For governments, this means recognizing that Indigenous communities are a part of the population to be appreciated and consulted, and whose full participation should be promoted at the local and national level," Francis told the Indigenous leaders Wednesday.

​Trump oversteps Obama

In the waning days of the Obama administration, federal agencies that have authority over the reservoir said they would not give permission for pipe to be laid until an environmental study was done. Trump, who had long signalled his support for the pipeline, last month instructed the U.S. Army Corps of Engineers to proceed with construction.

Pope Francis insisted Wednesday that Indigenous people must give prior consent for any economic activity on their ancestral lands (Alessandra Tarantino/Associated Press) Francis, history's first Latin American pope, has been a keen backer of Indigenous rights and has frequently spoken out about their plight.

The pipeline dispute has led to protests and clashes in recent months that have resulted in some 700 arrests.