As unidentified US and British officials said it appeared the plane was shot down by Tehran, most likely in an accident, Mr Trudeau stood before the cameras to call for a full investigation, and to reveal what he had been told by intelligence officials.

“We have intelligence from multiple sources... the intelligence indicates that the plane was shot down by an Iranian surface-to-air missile,” he said. “This may well have been unintentional.”

He added: “The intelligence evidence suggests very clearly a possible and probable cause for the crash.”

British prime minister Boris Johnson, later echoed Mr Trudeau’s comments. “There is now a body of information that the flight was shot down by an Iranian Surface to Air Missile. This may well have been unintentional,” he said in a statement, adding that four Britons were among the 176 people who lost their lives.

Iran plane crash: Ukraine Boeing 737 comes down near Tehran Show all 18 1 /18 Iran plane crash: Ukraine Boeing 737 comes down near Tehran Iran plane crash: Ukraine Boeing 737 comes down near Tehran People stand near the wreckage after a Ukrainian plane carrying 176 passengers crashed near Imam Khomeini airport in Tehran ISNA/AFP via Getty Iran plane crash: Ukraine Boeing 737 comes down near Tehran People and rescue teams are pictured amid bodies and debris All 176 people on board a Ukrainian passenger plane were killed when it crashed shortly after taking off, Iranian state media reported ISNA/AFP via Getty Iran plane crash: Ukraine Boeing 737 comes down near Tehran One of the engines State news agency IRNA said 167 passengers and nine crew members were on board the aircraft operated by Ukraine International Airlines Iran Press via Reuters Iran plane crash: Ukraine Boeing 737 comes down near Tehran Rescue teams work at the scene AFP via Getty Iran plane crash: Ukraine Boeing 737 comes down near Tehran Passengers' belongings West Asia News Agency via Reuters Iran plane crash: Ukraine Boeing 737 comes down near Tehran Members of the International Red Crescent collect bodies of victims EPA Iran plane crash: Ukraine Boeing 737 comes down near Tehran Rescue teams work amidst debris AFP via Getty Iran plane crash: Ukraine Boeing 737 comes down near Tehran A relative of a victim reacts at Boryspil International Airport, outside Kiev Reuters Iran plane crash: Ukraine Boeing 737 comes down near Tehran Rescue workers search the scene where a Ukrainian plane crashed in Shahedshahr, southwest of the capital Tehran, Iran, Wednesday, Jan. 8, 2020. A Ukrainian airplane with more than 170 people crashed on Wednesday shortly after takeoff from Tehran's main airport, killing all onboard. (AP Photo/Ebrahim Noroozi) Ebrahim Noroozi AP Iran plane crash: Ukraine Boeing 737 comes down near Tehran TOPSHOT - People and rescue teams are pictured amid the wreckage after a Ukrainian plane carrying 176 passengers crashed near Imam Khomeini airport in the Iranian capital Tehran early in the morning on January 8, 2020, killing everyone on board. - The Boeing 737 had left Tehran's international airport bound for Kiev, semi-official news agency ISNA said, adding that 10 ambulances were sent to the crash site. (Photo by Rouhollah VAHDATI / ISNA / AFP) (Photo by ROUHOLLAH VAHDATI/ISNA/AFP via Getty Images) ROUHOLLAH VAHDATI ISNA/AFP via Getty Iran plane crash: Ukraine Boeing 737 comes down near Tehran Rescue workers carry the body of a victim of an Ukrainian plane crash in Shahedshahr, southwest of the capital Tehran, Iran, Wednesday, Jan. 8, 2020. A Ukrainian airplane carrying 176 people crashed on Wednesday shortly after takeoff from Tehran's main airport, killing all onboard. (AP Photo/Ebrahim Noroozi) Ebrahim Noroozi AP Iran plane crash: Ukraine Boeing 737 comes down near Tehran Part of the wreckage Iran Press via Reuters Iran plane crash: Ukraine Boeing 737 comes down near Tehran Debris of a plane belonging to Ukraine International Airlines, that crashed after taking off from Iran's Imam Khomeini airport, is seen on the outskirts of Tehran, Iran January 8, 2020. Nazanin Tabatabaee/WANA (West Asia News Agency) via REUTERS ATTENTION EDITORS - THIS IMAGE HAS BEEN SUPPLIED BY A THIRD PARTY WANA NEWS AGENCY West Asia News Agency via Reuters Iran plane crash: Ukraine Boeing 737 comes down near Tehran Rescue workers search the scene where an Ukrainian plane crashed in Shahedshahr, southwest of the capital Tehran, Iran, Wednesday, Jan. 8, 2020. A Ukrainian airplane carrying 176 people crashed on Wednesday shortly after takeoff from Tehran's main airport, killing all onboard. (AP Photo/Ebrahim Noroozi) Ebrahim Noroozi AP Iran plane crash: Ukraine Boeing 737 comes down near Tehran Rescue team work at the scene where an Ukrainian plane crashed in Shahedshahr, southwest of the capital Tehran, Iran, Wednesday, Jan. 8, 2020. A Ukrainian airplane carrying 176 people crashed on Wednesday shortly after takeoff from Tehran's main airport, killing all onboard. (AP Photo/Ebrahim Noroozi) Ebrahim Noroozi AP Iran plane crash: Ukraine Boeing 737 comes down near Tehran CORRECTS YEAR - Debris is seen from a plane crash on the outskirts of Tehran, Iran, Wednesday, Jan. 8, 2020. A Ukrainian airplane carrying at least 170 people crashed on Wednesday shortly after takeoff from Tehranâ€™s main airport, killing all onboard, state TV reported. (AP Photos/Mohammad Nasiri) Mohammad Nasiri AP Iran plane crash: Ukraine Boeing 737 comes down near Tehran Officials inspect the wreckage EPA Iran plane crash: Ukraine Boeing 737 comes down near Tehran Debris is seen from an Ukrainian plane which crashed as rescue workers search the scene in Shahedshahr, southwest of the capital Tehran, Iran, Wednesday, Jan. 8, 2020. A Ukrainian airplane carrying 176 people crashed on Wednesday shortly after takeoff from Tehran's main airport, killing all onboard. (AP Photo/Ebrahim Noroozi) Ebrahim Noroozi AP

The comments of the two leaders come after remarks from anonymous Western officials suggesting Flight 752 had been shot down by the Iranians, apparently in error, on the night they launched ballistic missiles on US-Iraqi bases in Iraq, and may have been anticipating a possible reprisal from Washington.

Donald Trump said the plane was flying in a “rough neighbourhood”, and that something very terrible happened”.

Adding to the growing evidence, the New York Times published video footage it said appears to show an Iranian missile hitting a plane close to Tehran’s airport at the same time Flight 752 stopped transmitting its radio signal.

“A small explosion occurred when a missile hit the plane, but the plane did not explode, the video showed,” the newspaper said.

“The jet continued flying for several minutes and turned back towards the airport.”

The developments came as tensions between the US and Iran had appeared to ease, after Mr Trump on Wednesday indicated Washington was not planning further military operations, following the targetted assassination of Iranian military leader Qassem Soleimani.

Video purports to show moment Ukrainian airliner is hit by missile over Iran

When Iran responded by firing missiles at two bases used by US troops in norther Iraq, there as widespread concern the situation may rapidly escalate. It remains to be seen how Iranian responsibility for the downing of Flight 752 – if Tehran was responsible, impacts the already tense situation.

If confirmed, the plane’s downing would darkly echo an incident from three decades ago, when a US ship,USS Vincennes, accidentally downed an Iranian passenger plane with the loss of 290 lives during another period of conformation between the two nations.

Earlier, Ukraine’s top security official said that a missile strike was considered to be one of the “main working theories” for the crash.

Oleksiy Danilov, secretary of Ukraine’s Security Council, said officials were in Iran with a brief to look for any possible missile debris or evidence of a rocket strike.

“A rocket strike, possibly a Tor missile system, is among the main working theories, since there is information on the internet about elements of a missile being found near the site of the crash,” he said.

Philip Ingram, a former British military intelligence officer, explained the possible delay in the US releasing its conclusions by saying announcing a “working confirmation” could be a way of “releasing very classified info without giving your capability away”.

“If the missile was of a certain size then the US has a satellite network that will pick up any launch,” he said. I

ran’s head of civil aviation, Ali Abedzadeh, was quoted by ISNA News Agency as saying that it was “impossible that a missile hit the Ukrainian plane”. “How can a plane be hit by rocket or missile [and then the pilot] try to turn back to the airport?”​

Speaking in Ottawa, Mr Trudeau demanded a full investigation and that he had spoken with Iranian foreign minister Mohammad Zarif. He also spoke to Ukraine president Volodymyr Zelensky

“I made it clear that Canadian officials must be granted access to Iran...to...participate in a thorough investigation,” he said.