The Ukrainian passenger plane that crashed shortly after taking off from Tehran’s international airport Wednesday was shot down by mistake by an Iranian anti-aircraft missile, Pentagon officials told Fox News.

Officials said U.S. intelligence increasingly points at the airliner being accidentally struck by a Russian-made missile, killing all 176 people on board the flight, just hours after Iran fired more than a dozen ballistic missiles targeting two military bases housing American and coalition troops.

"An absolute tragedy," one U.S. official told Fox News. "They just screwed up and it is tragic."

The revelations come as Ukrainian investigators reportedly are awaiting permission from Iranian authorities to examine the crash site and look for missile fragments. Iran's head of civil aviation was quoted by the ISNA News Agency as saying Thursday that "scientifically, it is impossible that a missile hit the Ukrainian plane, and such rumors are illogical," according to Reuters. Iranian officials have blamed a technical malfunction for the aircraft’s doom.

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The U.S. official told Fox News that a Russian-made SA15 missile, which is part of the Tor surface-to-air missile system, was the kind that brought down the aircraft. Russia delivered 29 Tor-M1 systems to Iran in 2007 as part of a $700 million contract signed in December 2005. Iran has displayed the missiles in military parades as well.

"A strike by a missile, possibly a Tor missile system, is among the main (theories), as information has surfaced on the internet about elements of a missile being found near the site of the crash," Oleksiy Danilov, secretary of Ukraine's Security Council, told Ukrainian media earlier. He did not elaborate on where he saw the information.

When asked Thursday about what could have happened to the Ukrainian International Airlines flight, President Trump said he didn't believe that a mechanical failure caused the plane crash.

"It was flying in a pretty rough neighborhood," he said. "Somebody could have made a mistake on the other side."

Danilov also said other possible causes under consideration for Wednesday's downing included a drone or another flying object crashing into the plane, a terrorist attack or an engine malfunction causing an explosion. However, no terror group has claimed responsibility for the attack and the plane was less than four years old.

The crash came just a few hours after Iran launched a ballistic missile attack against Iraqi military bases housing U.S. troops amid a confrontation with Washington over it killing an Iranian Revolutionary Guard general in a drone strike last week.

Newsweek was the first to report that the plane was mistakenly shot down by missiles.

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Gen. Abolfazl Shekarchi, the spokesman of the Iranian armed forces, earlier denied a missile hit the airplane in comments reported Wednesday by the Fars news agency. He dismissed the allegation as "psychological warfare" by foreign-based Iranian opposition groups.

The incident has similarities to the 2014 downing of Malaysia Airlines Flight 17 over eastern Ukraine.

All 298 passengers and crew on board flight MH17 from Amsterdam to Kuala Lumpur were killed on July 17, 2014, when a missile shattered the Boeing 777 midair, sending debris and bodies raining down onto farms and fields of sunflowers. The jet in 2014 was shot down by a Soviet-made missile over rebel-held eastern Ukraine, about 25 miles from the Russian border, where fighting had been raging for months between Ukrainian forces and Russian-backed separatists.

The National Transportation Safety Board [NTSB] announced Thursday night it "designated an accredited representative to the investigation of the crash." Boeing spokesman Paul Bergman told Fox News, "We are supporting the NTSB in the investigation per Annex 13 protocol." Annex 13 protocol refers to the Convention on International Civil Aviation's recommended practices for investigating aircraft incidents.

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An initial report prepared by Iran's Civil Aviation Organization said Thursday that the plane’s crew never made a radio call for help and was trying to turn back for the airport when it went down.

The Ukrainian International Airlines flight took off at 6:12 a.m. Wednesday, after nearly an hour's delay, from Tehran's Imam Khomeini Airport, the main airport for travelers in Iran. It gained altitude heading west, reaching nearly 8,000 feet, according to both the report and flight-tracking data.

Then something went wrong, though “no radio messages were received from the pilot regarding unusual situations,” the report said. In emergencies, pilots reach out to air-traffic controllers to warn them and to clear the runway for their arrival, though their first priority is to keep the aircraft flying.

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Eyewitnesses, including the crew of another flight passing above it, described seeing the plane engulfed in flames before crashing at 6:18 a.m., the report said. Flight-tracking data for the plane stopped before the crash, which occurred in the town of Shahedshahr to the northeast of the plane's last reported position.

The crash caused a massive explosion when the plane hit the ground, likely because the aircraft had been fully loaded with fuel for the flight to Kyiv, Ukraine.

But the report also confirmed that both of the “black boxes” that contain data and cockpit communications from the plane had been recovered, though they sustained damage and some parts of their memory were lost. It also said that investigators have initially ruled out laser or electromagnetic interference as causing the crash.

"We insist Iran give us full access to the investigation and to the materials of the investigation and I call on everyone to avoid any speculations," Sergiy Kyslytsya, Ukraine's deputy minister for foreign affairs, said Thursday.

Oleksandr Zaporozhchenko, a mechanic with the Ukraine International Airlines in 2016-2018, said he knew one of the crew members of the plane and had never heard any complaints about the aircraft.

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“It is one the most reliable planes out there,” Zaporozhchenko told The Associated Press.

The plane was carrying 167 passengers and nine crew members from several countries, including 82 Iranians, at least 63 Canadians and 11 Ukrainians, according to officials. Many of the passengers were believed to be international students attending universities in Canada; they were making their way back to Toronto by way of Kiev after visiting with family during the winter break.

Fox News' Jennifer Griffin, Ben Evansky, Travis Fedschun, Dan Springer and The Associated Press contributed to this report.