Iran acknowledges its troops shot down a passenger jet and killed 176 people, describing a string of colossal failures

• A new report from Iran's Civil Aviation Organization indicates that a string of massive failures led Iran's military to shoot down a passenger jet and kill 176 people early this year.
• The Iranian report says the country's military shot down Ukraine International Airlines Flight 752 in January because of human error, an improperly calibrated air-defense system, communication problems, and a breach of engagement protocols.
• Following the release of the report, Ukraine said it was not ready to accept Iran's explanation for what happened.

A chain of serious mistakes led Iranian troops to fire on a passenger jet early this year, killing 176 people, a new report from Iran's Civil Aviation Organization indicates.

The report says the Iranian military shot down Ukraine International Airlines Flight 752 in January because of human error, an improperly calibrated air-defense system, communication problems, and a breach of engagement protocols, specifically firing without authorization.

The flight went down shortly after takeoff from Imam Khomeini International Airport on January 8. While Iran initially claimed engine failure was to blame, it acknowledged days later, following reported foreign intelligence on the actual cause, that the passenger aircraft was shot down by a pair of surface-to-air missiles.

The downing of Flight 752 happened just hours after the Iranian military fired more than a dozen ballistic missiles at US and coalition troops in Iraq in retaliation for the US drone strike one week earlier that killed one of Iran's most powerful leaders, Maj. Gen. Qassem Soleimani.

In the days that followed, Iran's Revolutionary Guard said it was on high alert when Flight 752 was shot down, with one commander saying Iran was "totally prepared for a full-fledged war."

'Such a failure initiated a hazard chain'

In that heightened state of alert, the report from Iran's Civil Aviation Organization says, responsibility for air-traffic control was transferred from civilian authorities to the military, which cleared Ukraine International Airlines Flight 752 to take off for its return trip to the Ukrainian capital, Kyiv.

Once in the air, though, Flight 752 "was identified by one of the air defense units as a threat and targeted consequently," the new report said.

An air-defense system that was moved was not recalibrated for its new position because of "human error" and was 107 degrees off, the report said, a major mistake that made it appear a passenger jet ascending from Tehran's airport was a potential military target approaching the capital from the southwest. The report said "such a failure initiated a hazard chain."

The air-defense unit operator relayed the information to the coordination center, but, for reasons not presented in the report, the notification was not communicated successfully.

The operator, who was said to be unaware of the calibration issue, then independently analyzed the information and concluded that the detected target was a threat.

Without receiving authorization from the coordination center, the report said, the air-defense unit operator opened fire on the aircraft, a violation of procedure. Two missiles were fired.

The passenger jet caught fire after it was hit and turned right toward the airport before crashing into a playground. The plane is believed to have exploded when it hit the ground.

"The aircraft," the report said, "then kept hitting the ground and bouncing on a route towards the airport, making the aircraft pieces, victims' properties, objects and body remains disintegrate completely in a vast area."

Ukraine's foreign minister on Tuesday said the country still had a lot of unanswered questions and was not yet ready to accept Iran's explanation.

"I want to clearly emphasize: It is early to say that the plane was shot down as a result of human error, as the Iranian side claims," Foreign Minister Dmytro Kuleba said Tuesday. He added that "we have many questions, and we need a large number of authoritative, unbiased, objective answers about what happened."

He insisted that Ukraine "will do all we can so that Iran pays the highest price" for what happened. Iran is said to have agreed to compensate the families of foreign victims for their loss. Nearly half the people aboard the plane were Iranian, but citizens of Canada, Ukraine, Sweden, Afghanistan, and the UK were also aboard the plane.

The report from Iran's Civil Aviation Organization said the country had learned its lesson and that the likelihood of a repeat of the Flight 752 tragedy was "improbable."