The whispers followed Muslim teacher Adil Charkaoui for months as young Quebeckers who crossed his path headed off to join overseas jihadi groups. Those murmurs suddenly turned into shouts when a member of the Parti Québécois called Mr. Charkaoui a "merchant of hate" and directly accused him of indoctrinating young extremists.

The arrest of 10 young people who police say tried to leave Montreal to join the terrorist group Islamic State has placed renewed scrutiny on Mr. Charkaoui, who became a religious teacher and leader of a community centre after years under surveillance and in detention as a terrorism suspect.

In the National Assembly, where members have immunity against defamation lawsuits, PQ MNA Agnès Maltais on Thursday said aloud what until now was limited to insinuation by Mr. Charkaoui's hardline anti-Islamist critics. She accused Mr. Charkaoui of indoctrinating more than 20 Montreal youth who have left Quebec to join militant groups or were stopped by police as they tried to leave.

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Each time Quebec youth try to leave "there is one point in common, one individual – Adil Charkaoui," Ms. Maltais said. "What is going on at that centre? What is Adil Charkaoui telling the children who attend? How is it that children who attend his centre and hear his teaching have a sudden desire to join the Islamic State?"

Reached on Thursday, Mr. Charkaoui referred requests for comment to a short message on his Facebook page: "With her irresponsible speech, Ms. Maltais is acting as an agent of radicalization, as the PQ has since 2013" when it proposed a charter of Quebec values that would limit religious expression in the province's public service.

Ms. Maltais demanded the Liberal government intervene with the Muslim community centre Mr. Charkaoui leads, Islamic Community Centre of Montreal East.

She did not suggest exactly what the provincial government could do.

Early this year, seven Quebec youth travelled to Turkey and then joined jihadi forces.

Two were said to have attended lectures by Mr. Charkaoui. One of the 10 arrested at Montreal's Trudeau airport last weekend is reported to have been enrolled in community centre courses.

An 11th person was arrested at a Montreal home on the weekend.

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Mr. Charkaoui has denied any role in radicalizing the youth. He recently told The Globe and Mail he is the victim of a witch hunt. "It's a new form of McCarthyism," he said.

"It's this social climate that is radicalizing people. Instead of telling Muslims they are partners, they are telling them they are suspects."

Ms. Maltais's accusation against Mr. Charkaoui ignored a second connection many of the young people shared: At least 11 of them are known to have attended Collège de Maisonneuve, a junior college that is part of Quebec's CEGEP system, which most teenagers attend after high school. (Mr. Charkaoui once rented space from the college, but was not employed there.)

College officials have made their own denial, saying indoctrination happens outside of school and on social media.

Provincial Public Security Minister Lise Thériault refused to single out Mr. Charkaoui or the school, saying: "Ninety per cent of these youth are radicalized on the Internet from the comfort of their own home."

Born in Morocco, Mr. Charkaoui arrived in Canada in the 1990s and was arrested in 2003 under an immigration security certificate on suspicion of having attended an Islamist training camp in Afghanistan.

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After six years under surveillance and in detention, he successfully challenged the certificate in 2009.

Lawyers representing the Canadian Security Intelligence Service refused to turn over any evidence they had against him. Mr. Charkaoui is suing the federal government.

"The fact I got my citizenship [in 2014] signed by the Honourable Prime Minister Stephen Harper with a letter of congratulations shows there's no evidence I'm threat to national security," Mr. Charkaoui said in March.

Earlier this spring, The Globe interviewed a half dozen of Mr. Charkaoui's former and current students.

Each denied he has ever talked up jihad or endorsed the Islamic State.

"All he does really is explain what's in the [Koran]. So that someone doesn't read the book and misinterpret it," said one youth who did not want his name published.

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But even Mr. Charkaoui's allies say he can be his own worst enemy, using angry, divisive rhetoric to lash out against perceived injustice. "You may like or dislike some of what he says, but that's what we are. He has the right to say what he has to say," said Salam Elmenyawi, head of the Muslim Council of Montreal.

Mr. Harper was at Trudeau airport on Thursday to speak about plans to boost security programs to counter the terrorist threat. He expressed sympathy for families dealing with youth extremists, but shifted to a harder line.

"We have a beautiful country, a country that is democratic, free, open, tolerant.

"There is no excuse, no reason for a Canadian to become a jihadist or a terrorist. It's unacceptable in our country," he said.