A UN committee on women's rights on Thursday urged Canada to address discrimination in a law that has effectively stripped tens of thousands of descendants of indigenous women of their identities and rights.

In a report, the UN Committee on the Elimination of Discrimination against Women called on Ottawa to amend the Indian Act "to provide registration to all matrilineal descendants on an equal basis to patrilineal descendants."

The legislation has been the primary law used to administer Canada's indigenous peoples since 1876.

Ottawa insists that several improvements have been made to the act since 1985 that have eliminated "sex-based inequities."

But the UN committee said in a statement that gender-based discrimination has not been fully addressed and "continues to affect tens of thousands of descendants of indigenous women today."

"The entire issue stems from the disrespect of indigenous people's fundamental right to self-identification," said committee member Corinne Dettmeijer.

"It is further exacerbated by the unequal criteria by which men and women are permitted to transmit indigenous status and identity to their descendants."

"By comparison, descendants of indigenous Indian grandfathers would never have lost their status and have always been able to pass on their status to their children," Dettmeijer added.

Prime Minister Justin Trudeau's government has championed indigenous reconciliation, including moving to align Canadian laws with the United Nations declaration on Indigenous rights.

But he's acknowledged there is more to be done.

Discrimination against indigenous peoples has rocked Canada, notably after recent discoveries of more than 1,500 unmarked graves at former residential schools that indigenous children were once forced to attend.

A truth and reconciliation commission in 2015 estimated that more than 4,000 of the 150,000 students enrolled from the late 1800s to the 1990s in these schools - isolated from their families, language and culture - had died of disease, malnutrition and neglect.

It concluded the failed government policy of assimilation amounted to "cultural genocide."