But he didn't offer the apology sought by the Canadian prime minister.

Francis, in remarks to faithful gathered in St. Peter's Square on Sunday, also called on the authorities to foster healing but made no reference to Prime Minister Justin Trudeau's insistence, two days earlier, that the Vatican apologise and take responsibility.

From the 19th century until the 1970s, more than 150,000 indigenous children were forced to attend state-funded Christian schools, the majority of them run by Roman Catholic missionary congregations, in a campaign to assimilate them into Canadian society.

The Canadian government has admitted that physical and sexual abuse was rampant in the schools, with students beaten for speaking their native languages.

Ground-penetrating radar was used to confirm the remains of the children at the Kamloops Indian Residential School in Kamloops, British Columbia, last month. The school was Canada's largest such facility and was operated by the Catholic Church between 1890 and 1969.

"I am following with pain the news that arrives from Canada about the upsetting discovery of the remains of 215 children," Francis said in his customary Sunday noon remarks to the public.

"I join with the Canadian bishops and the entire Catholic Church in Canada in expressing my closeness to the Canadian people traumatised by the shocking news," Francis said.

"This sad discovery adds to the awareness of the sorrows and sufferings of the past," he added.

Trudeau on Friday blasted the church for being "silent" and "not stepping up," and called on it to formally apologise and to make amends for its prominent role in his nation's former system of church-run indigenous boarding schools.

Francis' comments spoke of healing but not of apology.

"May the political and religious authorities continue to collaborate with determination to shed light on this sad affair and to commit humbly to a path of reconciliation and healing," Francis said.

Australian Associated Press