Amid mounting international pressure, Iran on Saturday said its military "unintentionally" fired a missile at a Ukrainian passenger plane because of "human error."

The Ukraine International Airlines airliner had flown close to a sensitive military site when it was brought down, reported Iranian state TV, citing a statement from Iran's armed forces.

Iranian authorities had initially denied shooting down the aircraft. The about-face came after several Western leaders said early evidence suggested a missile was behind the crash.

Read more: Germany, world leaders react after Iran admits downing plane by 'mistake'

The plane, en route to the Ukrainian capital of Kyiv, was carrying 167 passengers and nine crew members from several countries, including 82 Iranians, 57 Canadians and 11 Ukrainians, according to officials.

Later on Saturday, Iranian investigators said that the aircraft's black box recorders would be sent to France for analysis. France was decided on as a neutral party after it was determined that Iran does not have the necessary technology and Canada, France, and the US all refused to send equipment to Iran.

'Mistaken for a hostile target'

According to the Iranian military's statement, the plane was mistaken for a "hostile target'' after it turned toward a "sensitive military center'' of the Revolutionary Guard. Iran's military forces were at their "highest level of readiness," after the US killed the Iranian General Qassem Soleimani in an airstrike in Baghdad.

"In such a condition, because of human error and in an unintentional way, the flight was hit,'' the statement said, apologizing for the disaster and saying that the country would upgrade its systems to prevent such "mistakes'' in the future.

The military statement said those responsible would be held accountable.

Read more: Ukraine Airlines crash: Victims' relatives demand answers

Iranian news agency Fars reported that the country's supreme leader, Ayatollah Ali Khamenei, Iran's highest authority, was told about the cause of the crash on Friday and, following a meeting with security officials, ordered the information to be shared publicly.

Khamenei called on the military to "pursue probable shortcomings and guilt in the painful incident."

Shortly after, a commander of the Iranian Revolutionary Guard said on state television that his aerospace unit takes full responsibility for the crash.

"I take full responsibility and I will obey whatever decision is taken," said Brigadier General Amirali Hajizadeh. "I would prefer to die rather than witness such an incident."

"The disaster occurred after a communications problem, but that is no justification and is unforgivable," said Hajizadeh.

'Disastrous' and 'unforgivable'

In a tweet, Iranian President Hassan Rouhani expressed regrets over the plane's downing.

"The Islamic Republic deeply regrets this disastrous mistake," he said. "Investigations continue to identify & prosecute this great tragedy & unforgivable mistake."

Iranian Foreign Minister Mohammad Javad Zarif also expressed his sorrow over the downed jet, but added that the US shared blame for the disaster.

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

A few hours after Iran's admission, Ukrainian President Volodymyr Zelenskiy in a Facebook post insisted that the Islamic Republic punish those who were guilty, pay compensation, and fully cooperate with international investigators, among other demands.

"We expect Iran... to bring the guilty to the courts," he wrote.

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kp, es/dr (AFP, AP, Reuters)

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