OTTAWA (Reuters) - Iran is not conducting its investigation into the downing of a civilian airliner in January properly and many questions remain unanswered, an independent Canadian report into the tragedy said on Tuesday. The 79-page document is the latest expression of frustration from Western nations into how the Islamic Republic is handling the aftermath of a disaster that claimed 176 lives. Iran’s Revolutionary Guards say they accidentally shot down the Ukraine International Airlines plane shortly after take-off, mistaking it for a missile when tensions with the United States were high. Many of the victims were Canadian citizens or permanent residents. Former Canadian cabinet minister Ralph Goodale, charged with helping the victims’ families and examining how to deal with similar disasters in future, said “many of the key details of this horrific event” remain unknown. “Iran...has not conducted its investigations (safety, criminal or otherwise) in a truly independent, objective and transparent manner, and answers to critical questions” are absent, he wrote in the report. Last month the United Nations aviation agency and Ukraine complained separately about how Iran was conducting the probe. “There’s not much of a track record to base any optimism on so far,” Goodale said by phone when asked about the chances of Tehran carrying out a fully transparent investigation. Just before the disaster, Iran had fired missiles at U.S. bases in Iraq. Five days earlier, the United States had killed a Revolutionary Guards commander in Iraq. Goodale said Iran needed to explain how it had assessed the risks to civilian aircraft, why it had left the airspace open and also why the Guards had decided to down the plane. Canada and other nations who lost citizens are pressing Iran for reparations and a formal apology. “Canada just has to be absolutely relentless...to make sure the international community does not forget what happened,” said Goodale.