Updated below

The Iranian Armed Forces General Staff just admitted (in Farsi, English translation) that its air defenses inadvertently shot down the Ukrainian flight PS 752 shortly after it took off on January 8 in Tehran :

2- In early hours after the missile attack [on US’ Ain al-Assad base in Iraq], the military flights of the US’ terrorist forces had increased around the country. The Iranian defence units received news of witnessing flying targets moving towards Iran’s strategic centres, and then several targets were observed in some [Iranian] radars, which incited further sensitivity at the Air Defence units.

3- Under such sensitive and critical circumstances, the Ukrainian airline’s Flight PS752 took off from Imam Khomeini Airport, and when turning around, it approached a sensitive military site of the IRGC, taking the shape and altitude of a hostile target. In such conditions, due to human error and in an unintentional move, the airplane was hit [by the Air Defence], which caused the martyrdom of a number of our compatriots and the deaths of several foreign nationals.

4- The General Staff of the Armed Forces offers condolences and expresses sympathy with the bereaved families of the Iranian and foreign victims, and apologizes for the human error. It also gives full assurances that it will make major revision in the operational procedures of its armed forces in order to make impossible the recurrence of such errors. It will also immediately hand over the culprits to the Judicial Organization of the Armed Forces for prosecution.

The Pentagon had claimed that Iran shot down the airliner but the evidence it presented was flimsy and not sufficient as the U.S. tends to spread disinformation about Iran.

It is welcome that the Iranian forces come clean about the incident.

That is not a given in such cases.

After the USS Vincennes in 1988 had shot down Iran Air Flight 655 and killed 290 people, including many children, the U.S. government denied any culpability. George H. W. Bush, the vice president of the United States at the time, commented: "I will never apologize for the United States – I don't care what the facts are... I'm not an apologize-for-America kind of guy." Despite its "error" the crew was given medals and the captain was even awarded a Legion of Merit "for exceptionally meritorious conduct in the performance of outstanding service as commanding officer ...".

We can be assured by the statement of Iran's president that the responsible Iranian officer will receive no such a reward:

Hassan Rouhani @HassanRouhani - 

4:43 UTC · 11 Jan 2020

Armed Forces’ internal investigation has concluded that regrettably missiles fired due to human error caused the horrific crash of the Ukrainian plane & death of 176 innocent people.
Investigations continue to identify & prosecute this great tragedy & unforgivable mistake. #PS752

The Islamic Republic of Iran deeply regrets this disastrous mistake.

My thoughts and prayers go to all the mourning families. I offer my sincerest condolences.

Let us also not forget that the root cause of the accident was an assassination campaign which the U.S. launched against foreign military commanders of a country with which it is not at war:

On the day U.S. forces killed Soleimani, they launched another secret operation targeting a senior Iranian official in Yemen

The strike targeting Abdul Reza Shahlai, a financier and key commander of Iran’s elite Quds Force who has been active in Yemen, did not result in his death, according to four U.S. officials familiar with the matter.

The U.S. executed a long planned campaign against several Iranian officers in third countries without any reasonable justification:

“There is no doubt that there were a series of imminent attacks being plotted by Qasem Soleimani,” Secretary of State Mike Pompeo told Fox News on Friday. “We don’t know precisely when and we don’t know precisely where, but it was real.” Gen. Mark Milley, chairman of the Joint Chiefs of Staff, and Defense Secretary Mark T. Esper have likewise supported the case for an imminent plot.

“Did it exactly say who, what, when, where? No,” Milley told reporters this week. “But he was planning, coordinating and synchronizing significant combat operations against U.S. military forces in the region, and it was imminent.”

Can there be any "imminent threat" when one does not know the "who, what, when, where" of the threat? Why would killing a high officer prevent the execution of such a threat? The excuse is obviously bullshit.

It were the U.S. assassination of the Iraqi and Iranian national heroes Abu Mahdi al-Muhandes and Major General Qassem Suleimani that led to the high alarm and nervousness which, in the end, killed 176 passengers and crew on board of flight PS 752.

Iran's foreign minister is right to point that out:

Javad Zarif @JZarif - 

4:05 UTC · 11 Jan 2020

A sad day. Preliminary conclusions of internal investigation by Armed Forces:

Human error at time of crisis caused by US adventurism led to disaster

Our profound regrets, apologies and condolences to our people, to the families of all victims, and to other affected nations.