(CNN) Iran unintentionally shot down the Ukrainian plane that crashed near Tehran this week, killing 176 people, the nation's state media reported.

The general staff of Iran's armed forces said the crash Wednesday was due to human error. Iran targeted the passenger plane unintentionally, Press TV said.

"A sad day. Preliminary conclusions of internal investigation by Armed Forces: Human error at time of crisis caused by US adventurism led to disaster," Iranian Foreign Minister Javad Zarif tweeted. "Our profound regrets, apologies and condolences to our people, to the families of all victims and to other affected nations."

Fragments of the plane had been taken to a hangar off-site to "reconstruct" it for the investigation, said Ali Abedzadeh, the head of Iran's Civil Aviation Authority. The victims' remains have been sent to a forensic lab for DNA testing.

Debris, including passengers' personal items, at the scene.

US Secretary of State Mike Pompeo has said Washington believes it is "likely" Iran was responsible for the downing of the Boeing 737-800 and that an "appropriate response" would come when a "final determination" is made.

CNN obtained a video that appears to show a missile strike an object in Tehran's night sky, around the same time that the Ukrainian plane crashed early Wednesday, and separate footage that captures the moment of the crash.

The crash came just hours after Iran fired missiles at Iraqi military bases housing US troops in retaliation for a drone strike at Baghdad airport that killed Iranian commander Qasem Soleimani, who was one of Iran's most powerful and influential military leaders.

Hours after the missile operation in Iraq, US military flights around Iranian borders increased and Iranian military officials reported seeing aerial targets coming toward Iran's strategic centers, according to a statement released by Iranian armed forces headquarters.

Defense centers around Iran reported seeing increased radar activity which caused a heightened sensitivity in the aerial defense centers of the country, the statement reads.

The Ukrainian flight took off from Imam Khomeini Airport and came close to a sensitive Islamic Revolutionary Guard Corps military center at an altitude and flight condition that resembled hostile targeting, which led to it getting unintentionally hit, it added.

Iranian authorities are in possession of the two flight data recorders, also known as black boxes, which Prystaiko said Ukrainian investigators have seen but don't have access to. He added that Iran was, however, cooperating, and that he expected Ukraine could "extract and analyze" the data and recordings.

The last words of the pilot were "peaceful and that everything was OK," he said.

Prystaiko said Ukrainian investigators have access to the recording of the conversation between the control tower and the Ukrainian International Airlines crew.

The recent escalated hostilities between the US and Iran have complicated the thorny task of investigating the crash. US government investigators, for example, cannot fly into Tehran and meet with government officials without a license. That prohibition is due to longstanding sanctions rather than the most recent events, according to two US officials who spoke on the condition of anonymity.

Pompeo and Treasury Secretary Steven Mnuchin announced on Friday that President Donald Trump was authorizing yet more sanctions on Iran.

The Iranian government, which under international protocol has control of the investigation, had earlier said it would not work with the US or Boeing in the probe, but on Friday reversed its position.

If Iranian authorities are unable to reconstruct and analyze the information from the fight data recorders, they said they would seek help from international partners Russia, France, Canada or Ukraine.

Ukrainian investigators were given access to the black boxes on Friday, according to Ukraine's foreign minister, but had yet to start examining the information, which includes recordings of communications between the pilot and Tehran flight control.

Photos: Ukrainian plane crashes in Iran Bodies are recovered by emergency crews at the scene of a plane crash in Iran on Wednesday, January 8. Hide Caption 1 of 30 Photos: Ukrainian plane crashes in Iran At Ukraine's Boryspil International Airport, flowers are placed at a memorial for the nine crew members who were killed in the crash. Hide Caption 2 of 30 Photos: Ukrainian plane crashes in Iran The partner of crew member Julia Sologub kisses a portrait of her at the airport memorial in Ukraine. Hide Caption 3 of 30 Photos: Ukrainian plane crashes in Iran A Ukraine International Airlines employee lights a candle that is part of a symbolic runway at the airport memorial. Hide Caption 4 of 30 Photos: Ukrainian plane crashes in Iran Mourners place candles and photographs outside the Alberta Legislature Building during a vigil in Edmonton, Alberta. Hide Caption 5 of 30 Photos: Ukrainian plane crashes in Iran A man reacts at the crash site. Hide Caption 6 of 30 Photos: Ukrainian plane crashes in Iran Rescuers work to recover debris from the plane. Hide Caption 7 of 30 Photos: Ukrainian plane crashes in Iran A child's shoe is pictured at the scene of the crash. Hide Caption 8 of 30 Photos: Ukrainian plane crashes in Iran A man observes a piece of the wreckage. Hide Caption 9 of 30 Photos: Ukrainian plane crashes in Iran Crews search the scene. Hide Caption 10 of 30 Photos: Ukrainian plane crashes in Iran An official stands near a piece of plane wreckage. Hide Caption 11 of 30 Photos: Ukrainian plane crashes in Iran Debris from the plane is seen as authorities work at the site of the crash. Hide Caption 12 of 30 Photos: Ukrainian plane crashes in Iran Emergency response teams and body bags are seen amid the debris. Hide Caption 13 of 30 Photos: Ukrainian plane crashes in Iran Victims' possessions are seen scattered at the crash site. Hide Caption 14 of 30 Photos: Ukrainian plane crashes in Iran Recovery crews carry the body of a victim. Hide Caption 15 of 30 Photos: Ukrainian plane crashes in Iran A rescuer stands amid the crash debris. Hide Caption 16 of 30 Photos: Ukrainian plane crashes in Iran Emergency crews search the scene of the crash. Hide Caption 17 of 30 Photos: Ukrainian plane crashes in Iran Pieces of the plane are strewn across the crash site. Hide Caption 18 of 30 Photos: Ukrainian plane crashes in Iran Authorities recover debris from the plane. Hide Caption 19 of 30 Photos: Ukrainian plane crashes in Iran Bystanders watch as emergency teams work the crash site. Hide Caption 20 of 30 Photos: Ukrainian plane crashes in Iran Emergency workers investigate the scene. Hide Caption 21 of 30 Photos: Ukrainian plane crashes in Iran An emergency worker passes part of the destroyed plane. Hide Caption 22 of 30 Photos: Ukrainian plane crashes in Iran Crews transport a victim's body from the scene. Hide Caption 23 of 30 Photos: Ukrainian plane crashes in Iran This aerial photo shows the crash site near the airport. Hide Caption 24 of 30 Photos: Ukrainian plane crashes in Iran Body bags are laid out at the crash site. Hide Caption 25 of 30 Photos: Ukrainian plane crashes in Iran Parts of the plane are seen strewn across the crash site. Hide Caption 26 of 30 Photos: Ukrainian plane crashes in Iran Authorities work through the plane's debris. Hide Caption 27 of 30 Photos: Ukrainian plane crashes in Iran Workers carry items retrieved from the scene. Hide Caption 28 of 30 Photos: Ukrainian plane crashes in Iran Rescue teams conduct a search. Hide Caption 29 of 30 Photos: Ukrainian plane crashes in Iran People stand near the wreckage. Hide Caption 30 of 30

The exchange of attacks between Tehran and Washington -- both on Iraqi soil -- marked a dramatic escalation of tensions between the adversaries and raised fears of another proxy war in the Middle East.

A US official familiar with the intelligence said the aircraft was downed by two Russian-made SA-15 surface-to-air missiles. The US saw Iranian radar signals lock onto the jetliner, before it was shot down.

The US increasingly believes this was accidental.

The US, Britain, Canada, Sweden and the European Commission have called for an independent and credible investigation.