KITCHENER -- Two students from the University of Waterloo and two from the University of Guelph are among the 176 passengers and crew killed after a Ukrainian passenger plane crashed near Iran's capital on Wednesday.

Flags are at half mast at the University of Waterloo, where Mari Foroutan and Mansour Esfahani were PhD students.

Engineering department graduate student Michelle Liu says she was emailing with Esfahani on Tuesday.

"It's devastating and shocking. You know, it's one of those things you don't think is going to happen to somebody you know and then it does," Liu says.

Matthew Grant, the University of Waterloo's director of media relations adds that it's not only a tough day for his university, but a tough day in general for academia in Canada.

Ghanimat Azhdari was one of the University of Guelph students killed in the crash. She was a PhD student in the department of geography, environment and geomatics. Azhdari was on her way back to Guelph after visiting family in Iran for the holidays, the university confirmed to CTV News on Wednesday morning.

Milad Ghasemi Ariani was also a Guelph student, and was working toward a PhD in the marketing and consumer studies program.

Dr. Faisal Moola worked closely with Azhdari, who had just wrapped up an international project with the United Nations in December.

"Just crushing. I'm in terrible pain," says Moola.

He adds that a number of the students aboard the Ukraine International Airlines flight came to Canada with such great aspirations to learn.

Sixty-three Canadians were killed after the flight crashed near Tehran.

Canada's Foreign Affairs Minister François-Philippe Champagne said in a statement on Twitter that the number of the Canadian deaths could change as more information, such as the number of dual citizens on the flight, becomes available.

The flight was headed to Kyiv, Ukraine.

It is still unclear what caused the Boeing 737 to go down.

Iranian officials say they suspect a mechanical issue is to blame. Ukrainian authorities are also investigating.

The plane's black boxes have been recovered, but there are reports that Iran is not handing them over to Boeing.