The pope made the comment while flying back to Rome after a week-long trip to Canada, where he delivered a historic apology for the Church's role in the policy.

He was asked by an indigenous Canadian reporter on the plane why he did not use the word genocide during the trip, and if he would accept that members of the Church participated in genocide.

"It's true that I did not use the word because I didn't think of it. But I described genocide. I apologised, I asked forgiveness for this activity, which was genocide," Francis said.

"I condemned this, taking children away and trying to change their culture, their minds, change their traditions, a race, an entire culture," the pope added.

Between 1881 and 1996 more than 150,000 indigenous children were separated from their families and brought to residential schools. Many children were starved, beaten and sexually abused in a system that Canada's Truth and Reconciliation Commission called "cultural genocide".

The schools were run for the governments by religious groups, most of them Catholic priests and nuns.

"Yes, genocide is a technical word but I did not use it because I did not think of it, but I described .... yes, it is a genocide, yes, yes, clearly. You can say that I said it was a genocide," he said.

Last Monday, Francis visited the town of Maskwacis, site of two former residential schools, where he apologized and called forced assimilation "evil" and a "disastrous error"

He also apologised for Christian support of the "colonizing mentality" of the times.