A suggestion that white and non-black protesters limit their visibility at protests Tuesday in Ottawa and Toronto against the fatal shooting of a black teen in Ferguson, Mo., has sparked a heated debate on social media.

Bilan Arte, one of the Ottawa event organizers, says on the vigil's Facebook page that "white/non black allies" should "refrain from taking up space" and "never be the centre of anything."

The same message appeared verbatim on the Facebook page for the Toronto rally, asking whites and non-blacks to not speak to the media, saying "black voices are crucial to this," and asking white and non-black protesters to "stand behind black folks or between us and the police."

In Ottawa, dozens of people -- some holding signs saying "black lives matter," "shame on the American justice system" and "racism exists" -- rallied outside the American embassy on Tuesday evening.

"Particularly tonight, we're talking about black lives, and we're talking about the experience of black people, which is different from the experience of other racialized folks," Arte said at the Ottawa vigil.

"We can't just say, 'Oh, we're doing an event, and it's going to be anti-racist, and it's going to be about centering black voices, but we're going to have people who don't necessarily identity with those experiences who are going to be at the front of the room, who are going to be the ones sharing the mic, who are going to be the ones speaking'," she added.

Arte's post prompted more than 190 comments, with one man asking "is this an anti-racist rally or a pro-segregation one?"

Arte, deputy chairwoman with the Canadian Federation of Students, says on her own Facebook page that she's received upwards of 50 messages from "righteous upset white people" taking issue with the post.

"I think her goal with that was just to get black people to speak for themselves," said protester Delisha Smith.

The protests in Toronto and Ottawa follow a decision Monday by a grand jury in the U.S. not to indict police officer Darren Wilson in the shooting death of 18-year-old Michael Brown, who was unarmed.

"I Know this is not America, this is Canada, but it can happen to any one of my brothers, any one of my cousins, any one of my friends, and if there's no justice, how do you want us to progress?" said Eddyson Pierre at the Ottawa vigil.

"For an 18-year-old child to be killed like that, I'm 18, and for a child to be killed like that, and for Darren Wilson to not be indicted is disgusting, and I won't stand for it," said protester Nima Hussein.

A riot followed and thousands of National Guardsmen have been called in to help prevent a second night of violence.

Also on Tuesday evening, demonstrators gathered outside the U.S. consulate in Toronto, shouting "being black is not a crime" and other slogans against police brutality, while others held a candlelight vigil.

With files from the Canadian Press