Canada's Justin Trudeau says Ukrainian airliner was shot down

Canadian Prime Minister Justin Trudeau says the Ukrainian airliner that went down on Tuesday night was shot down by Iranian surface-to-air missiles, adding that the hit could have been an accident. 

"It is now more important than ever that we know exactly how such a tragedy could have happened," Trudeau said, speaking to reporters at the National Press Theatre in Ottawa. 

Trudeau said Canada is working with its allies to ensure that an in depth investigation takes place.

Trudeau reiterated Canada's request to Iran to take part in its investigation, but implied Iranian authorities had not yet approved such a request. 

"We're working with Ukrainian investigators at this time and we are continuing to ask to have Canadians involved in this process and we will continue to have that conversation,"  Trudeau said. 

For the moment Iran plans to keep the black box from the crashed plane in Iran, Trudeau said, adding that Ukrainian authorities said they were told by Iran that their investigators would be allowed access to the box.