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U.S. intelligence officials have evidence that suggests that the Ukraine International Airlines jetliner that crashed in Iran on Wednesday, killing 176 people, was downed by an Iranian missile by mistake, multiple officials told NBC News.

A Western intelligence official told NBC News that there was high confidence that the plane was felled by an accidental missile strike. The source, who receives high-level briefings from U.S. intelligence agencies, said the evidence includes satellite imagery and communications intercepts.

"Not much goes on above head height in Iran without it being tracked," the source said.

Prime Minister Justin Trudeau said Canadian intelligence sources also pinned blame on Iran for what might have been an "unintentional" missile attack.

"We have intelligence from multiple sources, including our allies and our own sources. The evidence indicates that the plane was shot down by an Iranian surface-to-air missile," Trudeau told reporters in Ottawa. "This may well have been unintentional."

Trudeau sidestepped several questions asking whether Canada should blame the United States for its deadly attack on a top Iranian military leader, which has renewed tension between Tehran and Washington.

"I think that's one of the many questions that people will be thinking about and trying to find answers to," Trudeau said in French. "But for the moment, I just want to underline the importance of having a full and credible investigation so we can get those facts and we can continue to analyze based on these facts."

British Prime Minister Boris Johnson released a statement saying his thoughts were with the families of the four British nationals who were killed, and he echoed Trudeau's assertion that an Iranian mistake might have been responsible.

"There is now a body of information that the flight was shot down by an Iranian Surface to Air Missile," Johnson said. "This may well have been unintentional. We are working closely with Canada and our international partners and there now needs to be a full, transparent investigation."

An initial Iranian report released Thursday suggested that a sudden emergency struck the Boeing 737 before it went down just moments after having taken off from Imam Khomeini International Airport in Tehran. The report said the crew never made a radio call for help and were trying to turn back for the airport when the plane crashed.

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The Boeing 737 has several systems to announce itself to other aircraft and to ground-based air-traffic control. The 737 includes a state-of-the-art Automatic Dependent Surveillance-Broadcast, or ADS-B, system, which automatically transmits altitude, airspeed and location and generally indicates that an aircraft is not part of a military operation.

U.S. authorities told The Washington Post that the plane was likely hit by a SA-15 "Gauntlet" surface-to-air missile, a Russian-made system that's also known as Tor. The highly automated Tor system, which Russia has sold to Iran as recently as 2015, requires a three-person crew.

Tor missile systems are designed to be mobile and self-contained, meaning they can rely on their own radar system to detect targets, rather than connect to a larger integrated air-defense system that monitors civilian air traffic.

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A child's shoe at the scene of the crash of Ukrainian airliner near Imam Khomeini International Airport in Tehran on Wednesday. Borna Ghassemi / AFP - Getty Images

Flight 752 lifted off at the end of a tense week in which missile batteries were repositioned throughout Iran, possibly in anticipation of a U.S. attack. Anti-aircraft batteries are often the first things to be destroyed in an attack, placing the crews inside them under enormous psychological pressure. Radar crews are trained to use their equipment only briefly, as radar is easy to detect and target.

While the takeoff and steady climb of a passenger plane are obvious to an experienced crew watching it for several minutes on radar, and while even a civilian phone app like FlightAware could have identified the plane as a civilian aircraft from its ADS-B system, a crew on the ground outside Tehran may not have had enough radar time or access to civilian information systems to identify it accurately.

Investigators from Iran's Civil Aviation Organization have offered no immediate explanation.

President Donald Trump, asked Thursday for his thoughts on what happened, said, "Well, I have my suspicions."

"It's a tragic thing," Trump said. "Because somebody could've made a mistake on the other side. ... It was flying in a pretty rough neighborhood, and somebody could, could've made a mistake."

The plane was carrying 167 passengers and nine crew members from several countries, including 82 from Iran, at least 63 from Canada and 11 from Ukraine, according to officials.

Many of the passengers were believed to have been international students attending universities in Canada; they were making their way back to Toronto by way of Kyiv after having visited their families during the winter break.

The flight also carried newlyweds and a family of four. The passenger list included several teenagers and children, some as young as 1 or 2.

The jet crashed hours after Iran fired missiles at two Iraqi bases housing U.S. forces early Wednesday local time.