Toronto (CNN) Canadian Prime Minister Justin Trudeau emerged this week from a long holiday break to face a tragedy that may recast his nation's role on the global stage -- and its relationship with its powerful neighbor to the south.

The liberal leader already had greeted 2020 with a new look: a salt-and-pepper beard that sparked a public buzz.

Now, owing to the crash in Tehran of a Ukrainian International Airlines flight with 57 Canadians aboard , Trudeau has adopted a newly somber and authoritative tone as well, perhaps indicating a far deeper change as he embarks upon the first full year of his second term.

"The families want answers," he said Thursday as he revealed to the world that Iran may have inadvertently shot down the airliner, killing everyone on board. "I want answers, closure, transparency, accountability and justice ... This government will not rest until we get that."

Iran, facing mounting pressure -- from Trudeau, US President Donald Trump and other world leaders -- admitted Saturday that it mistakenly shot down the passenger jet. Officials blamed human error amid Iran's fear of US military aggression for the wreck that left 176 people dead.

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"Even if it's Iran, the blame is on USA. If President Trump hadn't ordered the drone strike on Soleimani, all this wouldn't happen, we wouldn't be here today grieving," Ardy Gharagozli told CNN before Iran had acknowledged downing the plan. As he spoke, Gharagozli clutched a photograph of family friends who died on Flight 752.

Indeed, some here in Canada's most populous city see the crash victims as collateral damage in an American-Iranian conflict still being waged -- and one in which Canada, where Trump is deeply unpopular , can no longer remain on the sidelines.

But those expecting rage and fury from this Prime Minister might be disappointed.

Trudeau did not lash out this week at the Trump administration, nor did he take an especially tough stand with Iran, stopping short of calling the tragedy an act of war.

"What Iran has admitted to is very serious. Shooting down a civilian aircraft is horrific. Iran must take full responsibility," Trudeau said during a Saturday news conference in Ottawa. "Canada will not rest until we get the accountability, justice and closure that the families deserve."

That must include discussion of bringing home Canadian victims' remains, financially compensating their families and nailing down how Iranian systems at-large allowed such a tragic accident to unfold, said Trudeau, noting he'd spoken directly with Iranian President Hassan Rouhani since Iran admitted downing the jet.

The Prime Minister, however, sidestepped questions about Canadian sanctions against Iran and any repercussions for its three-day lag in coming clean about the crash.

"I'm furious that there are Canadian families that have lost their parents, their children, their spouses. It's a huge tragedy for the entire country, not just for the Iranian community," Trudeau said.

"For many of those families, that has all been struck down out of the blue by a regime that they had fled in the past, that they believed they had gotten away from," he said. "This is an incident that is truly horrible, and I am angry, I am disappointed, but I am firmly committed to getting answers and compensation and help and justice for the victims."

Canadian Prime Minister Justin Trudeau speaks Thursday, January 9, during a news conference in Ottawa about the downed Ukrainian jetliner. At least 63 Canadians were killed.

Navigating politics in the US, Iraq and at home

As for the United States, Trudeau had declined days earlier to respond to questions about Trump's comment that the Ukrainian plane was "flying in a pretty rough neighborhood" when it fell from the sky Wednesday upon takeoff.

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"I'll let Mr. Trump's words stand for himself," said Trudeau, who weeks earlier got caught apparently sharing a laugh with other world leaders at Trump's expense at Buckingham Palace. The American President responded by calling Trudeau "two-faced."

Asked Saturday about Iran's mention of US tensions contributing to the environment in which it shot down the airliner, Trudeau demurred.

"I've had a number of conversations with the US President recently and will continue to," he said. "The reality is there have been significant tensions in that region for a long time ... and what we are calling for now is a deescalation."

Following the crash, the Canadian government considered the crisis an "all hands on deck right now" situation, with various agencies at work to respond, a Canadian government official told CNN. Trudeau also reached out to a variety of allies for help, the official said Friday.

"Frankly, we're working very closely with the Trump administration," the official said. "They offered their help. (Foreign) Minister (Francois-Philippe) Champagne just spoke with (US) Secretary (of State Mike) Pompeo."

Trudeau met face-to-face Friday with families of the victims. He has pledged to keep them informed. But many victims' relatives and friends who spoke to CNN said Trudeau should do more to press both Iran and the United States on the crash investigation.

"How are they going to respond to the parents of the children of the loss of their sons, daughters, husbands, wives. This is so surreal," said Rosie, a family friend of a victim who attended a vigil Thursday in Toronto. She asked CNN not to use her last name.

But Trudeau also must navigate his nation's posture in Iraq. Canada leads NATO's noncombat mission in the Middle Eastern hotspot, where several hundred Canadian soldiers are training Iraqi counterparts. The effort could be key to keeping ISIS at bay, especially since the US-led military coalition in the region temporarily stopped its anti-ISIS missions amid the hostility from Iran and the militias it supports.

but does not provoke Iran, with which Canada Huddled with ministers and advisers since the plane disaster, Trudeau has been trying to fashion a response that is forceful and gets Canadian officials on the groundbut does not provoke Iran, with which Canada has not had diplomatic relations for years.

The Canadian government has been waiting for Iran to issue visas so several of its officials waiting in Ankara, Turkey, can access to the crash site, Trudeau said Saturday. Iran's cooperation on this score will be among the "tangible examples" its leaders can offer to show their commitment to "real cooperation and real openness" in the investigation, he said.

How Trudeau proceeds will impact not only his standing in global affairs but also how he is received at home, where the consequences of the airliner catastrophe is sure to consume victims' loved ones -- and his government's attention -- for months and years to come.

"The Prime Minister is heartbroken, of course, but he's also focused," the Canadian government official said. "The Prime Minister knows and recognizes that it is his job to do all this and that the families are counting on him."