A girl and three young women left Canada to join ISIS in Syria after studying at the Al-Huda Islamic Institute in Mississauga, Ont. — a school whose sister institution in Pakistan is now connected to the mass shooting in California.

It's unclear exactly when the Canadian students travelled overseas, but sources have confirmed they all left in the last two years after attending the school founded by controversial female Islamic scholar Farhat Hashmi.

Hashmi's ultra-conservative teachings in lectures and online have faced criticism for promoting an extreme wifely subservience to a husband.

The school's founder, however, is not a Canadian resident, despite several media reports to the contrary, sources told CBC News. Hashmi has not been in Canada for three years, those sources said. And Al Huda Institute in Mississauga says it is deeply concerned that anyone associated with Al Huda may have later gone on to support violent extremism.

Around 160 students attend school

Al-Huda's Mississauga campus, listed as a private school on the Ontario Ministry of Education's website, opened in 2004. Roughly 160 students in kindergarten to Grade 6 attend classes every day.

A Ministry of Education spokesman said private schools are independent of the ministry and operate as private businesses or non-profit organizations.

"The ministry does not approve, accredit or fund any private schools," the ministry said in an email to CBC News.

But in the evenings and on weekends, teenagers and adults can take seminars there. It's those classes the four Canadians, who ranged in age from 16 to early 20s, took in recent years before leaving for Syria.

The oldest attended for three months in 2012.

She's been living in Syria since the summer of 2014, her sister told CBC News. The woman and her family are not identified in this story, because of concerns about their security.

"It's really scary and it's really dangerous — and if she gets caught she will get killed," the sister said.

More than 160 kindergarten to Grade 6 students attend the Mississauga school every day. On evenings and weekends, the school offers adult classes. (YouTube/Ahlehadithsgd)

Security officials intercepted the other three Canadians in Turkey after they disappeared in July 2014, according to RCMP.

The teens were taken into custody and brought back to Canada.

It's still unclear how those teens and the other Canadian woman became connected to ISIS and radicalized. One woman's family believe she was radicalized online by an Edmonton-based recruiter.

Tashfeen Malik, one of the San Bernardino, Calif., shooters, attended classes six days a week for more than a year at Al-Huda's Pakistan campus, a school spokeswoman told The Associated Press. But it is not known how, where or by whom she was radicalized.

CBC's John Lancaster looks into a group of young Canadian women who left the country to support ISIS. Three of them are from the GTA, and all studied at a Mississauga Islamic Centre. 2:46 It's also unclear how much contact, if any, the teens or women would have had with Hashmi.

But the founder of the school — and the one like it in Pakistan — regularly delivers lectures by audio link to the Mississauga campus, CBC has learned. Lectures can also be found through Hashmi's website.

School 'deeply disturbed' by allegations

RCMP officers recently visited the Mississauga school to ask about other former students.

Al-Huda's operations manager told CBC News that the school would help with the investigation in any way possible.

"This is the first that we are learning of such allegations and [we] are as deeply disturbed as anyone," Imraq Haq said in a statement. "We are very clear that terrorism is against Islamic teachings … and we emphasize that it is both a civic and religious duty to help keep Canada, and the world, safe from violent extremist ideologies."

Editor's Note: This story has been updated with additional reaction from the school and more information about one of the four students.