OTTAWA -- Prime Minister Justin Trudeau is set to address the nation Thursday afternoon amid multiple reports pointing the finger at Iran for the downing of a Ukraine International Airlines flight, killing all on board including 138 people who were headed to Canada.

The plane crashed minutes after taking off from Tehran's airport on Wednesday.

Among the hypotheses is that an Iranian air-defence missile shot the plane down, possibly by accident. Ukrainian officials have said that's on their list of potential causes for the crash.

Two U.S. officials told The Associated Press Thursday it was "highly likely" that an Iranian anti-aircraft missile downed the jetliner.

The officials, citing U.S. intelligence, spoke on the condition of anonymity to discuss sensitive information. They had no immediate information on intent.

Canadian officials have declined all comment so far, with Trudeau expected to provide the government's response.

On Wednesday, Trudeau told a press conference on Parliament Hill that the government couldn't rule out that the plane had been shot down, but he also cautioned it was too early to speculate on a cause of the crash that killed all 176 people on board, at least 63 who were Canadian citizens.

Earlier Thursday, U.S. President Donald Trump suggested he believes Iran was responsible, without laying direct blame.

"Somebody could have made a mistake on the other side," Trump said in a Washington news conference, noting the plane was flying in a "pretty rough neighbourhood."

"Some people say it was mechanical," Trump added. "I personally don't think that's even a question."

Iran's civil aviation authority is in charge of the investigation, under international rules for probes of such crashes. The organization said Thursday it had invited Canadian investigators from the Transportation Safety Board to join a growing team probing the crash.

Trudeau said Wednesday that Canada had pushed to be part of the Iranian-led investigation.

It wasn't clear from the Iranian statement if the plane's manufacturer, American-based Boeing, had been invited to take part in the investigation under International Civil Aviation Organization rules that are guiding the probe.

The announcement that Canadians will be involved in the examination came as Foreign Affairs Minister Francois-Philippe Champagne spoke to his Iranian counterpart about Wednesday's crash.

A summary of the phone call released Thursday morning by Global Affairs Canada said Champagne stressed to Mohammad Javad Zarif the need for Canadian officials to be allowed into Iran to provide consular services, help with identification of the deceased and to take part in the investigation.

The summary said Champagne insisted that Canada and Canadians have "many questions which will need to be answered."

The summary did not provide any details about Zarif's reaction to Champagne's demands and Champagne's office declined to provide any further information. A brief summary on the Iranian foreign ministry website only said the two "conferred on the recent crash of a Ukrainian plane in Tehran as well as other issues of mutual interest."

Canada severed diplomatic ties with Iran in 2012, when it labelled the country a state sponsor of terrorism.

The crash came after a week of soaring tensions in the Middle East, occurring just hours after Iran launched missile attacks on bases in Iraq where American and allied troops are stationed. Iran said the attacks were retaliation for the American killing of a top general near Baghdad last week.

Champagne also told Zarif that Canada condemned Iran's missile attacks against military bases in Iraq.

Canadian soldiers were present in one of those bases.