The Ukrainian airplane that crashed outside of Tehran on Tuesday was mistakenly struck down by an Iranian anti-aircraft missile system, U.S. weekly Newsweek reported Thursday, citing a Pentagon official and a senior American intelligence official.

According to Newsweek, who also spoke to an Iraqi intelligence official, the Ukraine International Airlines flight that was en route from the Iranian capital to Kiev, was hit by a Tor-M1 surface-to-air missile system.

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The U.S. National Transportation Safety Board has accepted an invitation from Iran to take part in its investigation into the crash, the agency confirmed late on Thursday.

Later on Thursday, Canadian Prime Minister Justin Trudeau said that his country has evidence which indicates that the Ukrainian plane Wednesday "was shot down by an Iranian surface-to-air missile."

He added that it may have been "unintentional" and noted an in-depth investigation is under way into the crash, which killed more than 60 Canadians.

Iran will allow experts from Ukraine as well as Boeing experts from the United States, France and Canada to investigate the crash, the head of the Iranian aviation authority, Ali Abedsadeh, said Thursday.

Iran has also formally invited the U.S. National Transportation Safety Board to take part in its investigation. "The NTSB has replied to our chief investigator and has announced an accredited representative," Farhad Parvaresh, Iran's representative at the International Civil Aviation Organization, part of the United Nations, told Reuters.

The NTSB declined comment. A person briefed on the matter confirmed the NTSB had agreed to take part but said it was unclear what if anything its representative would be able to do under U.S. sanctions.

Parvaresh said other countries including Ukraine and Canada had also been notified. He denied U.S. and Canadian claims that the jet had been shot down and said Iran was committed to a full and transparent investigation for the accident, which he described as a "tragedy and disaster" for everyone involved.

Three U.S. officials had earlier said they believe that the Ukrainian plane was shot down by an Iranian missile, citing satellite data.

According to satellite data, one U.S. official said, the Ukrainian International Airlines Boeing 737-800 bound for Kiev was airborne for two minutes after departing Tehran when the heat signatures of two surface-to-air missiles were detected.

That was quickly followed by an explosion in the vicinity of the plane, the official said. Heat signature data then showed the plane on fire as it went down.

Two U.S. officials, however, said that Washington believed the downing of the plane was accidental.

The Pentagon declined to comment on the issue.

Trump announces increased sanctions as Iran denies accusations

U.S. President Donald Trump said that the deadly crash could have been a mistake, adding that he had a terrible feeling about the downed airliner but offering no evidence.

"Somebody could have made a mistake," Trump told reporters at a the White House, adding that he had suspicions about the crash but giving no other details.

Trump also said he has approved increased sanctions on Iran after Teheran launched a missile strike on Iraqi bases housing American military personnel, but gave no other details. The plane crash came just a few hours after the missile strike.

"It's already been done. We've increased them. They were very severe, but now it's increased substantially," Trump told reporters at the White House. "I just approved it a little while ago with Treasury."

The head of Iran's of Civil Aviation Organisation denied "illogical rumors" that a Ukrainian airliner that crashed near Tehran had been hit by a missile, the semi-official news agency ISNA reported.

"Scientifically, it is impossible that a missile hit the Ukrainian plane, and such rumours are illogical," ISNA quoted Ali Abedzadeh as saying.

Earlier Thursday, the secretary of the Ukrainian Security Council, Oleksiy Danylov, said that one of the potential causes for the airplane's destruction that his country is probing is contact with a Russian-manufactured Tor M-1 system.

The incident, which claimed the lives of all 176 people on board, came after the U.S. killed last week the Iranian Revolutionary Guard's Quds Force commander, Qassem Soleimani – an attack that has sparked concerns that a new war will be waged in the Middle East.

Meanwhile, an initial Iranian investigative report said Thursday that the crew of the plane never made a radio call for help and was trying to turn back for the airport when the burning plane went down.

The Iranian report suggests that a sudden emergency struck the Boeing 737 operated by Ukrainian International Airlines early on Wednesday morning, when it crashed, just minutes after taking off from Imam Khomeini International Airport in Tehran.

Investigators from Iran's Civil Aviation Organization offered no immediate explanation for the disaster, however. Iranian officials initially blamed a technical malfunction for the crash, something initially backed by Ukrainian officials before they said they wouldn't speculate amid an ongoing investigation.

Ukraine's leader said Iranian President Hassan Rohani has assured him of full cooperation in investigating the fatal crash and that Iran would provide experts access to all data.

President Volodymyr Zelenskiy spoke with Rohani by telephone on Thursday.

A statement on the Ukrainian presidential website says: “The Iranian party assured full cooperation with a view to holding an objective investigation and finding out the causes of the tragedy. Hassan Rouhani stressed that Iran would provide the Ukrainian expert group with prompt access to all the necessary data.”

DPA contributed to this report.