New Delhi: A day after the deadly Ukrainian passenger plane crash, the Iranian government has declared January 9 as the day of national mourning.

The suspense over the devastating plane crash persists as Ukraine ruled out possibility of pilot error, while Iran refused to share the black box with either Boeing or the Americans, making the investigation difficult.

"Government expresses condolences to the families of our compatriots who died in Kerman during the funeral ceremony of slain commander Qassem Soleimani and in a plane crash this morning, the government declared January 9 a national mourning day," Iranian government spokesman Ali Rabiei wrote on Twitter.

Pilot mistake unlikely: Ukraine

A pilot error is unlikely to have caused the crash of Ukraine's Boeing 737 near Tehran, the vice president of operations at the Ukraine International Airlines said on Wednesday.

"We know, as of today, that the aircraft went to the altitude of 2,400 meters (7,874 feet). The crew mistake is minimal. We simply do not consider it. Considering their experience, it is very hard to say that it could somehow be about the crew," Igor Sosnovsky said at a briefing.

"All crew members had enough experience and flight hours," he added.

Evgeny Dykhne, the company president, said that the crashed aircraft was one of the best at the Ukraine International Airlines.

Iran refuses to share black box of crashed plane to Boeing, US

Iran, on the other hand, has refused to hand over the black box of the crashed Ukrainian plane either to Boeing or the Americans, a decision that could potentially create difficulties for the investigators, reports said.

Iran Civil Aviation Organization chief Ali Abedzadeh said "terrorism" had played no role in the crash, the BBC reported citing Iranian Mehr news agency.

Another official, Qasem Biniaz, blamed an engine fire. "Had the accident happened due to a missile strike, the plane would have exploded in the air," he told the IRNA news agency.

A Kiev-bound Ukrainian Boeing 737 passenger plane with 179 people on board crashed on Wednesday shortly after taking off from the Iranian capital of Tehran, killing all those aboard.

But the head of Iran's Emergency Medical Services, Pir-Hossein Koulivand, confirmed the latest toll saying that there had been 170 passengers, including 147 Iranians, and nine crew members on the Ukraine International Airlines flight PS752 that went down in the vicinity of Parand, a city in Robat Karim county, reports Press TV.

Ukraine President orders creation of crisis team

Ukrainian President Volodymyr Zelensky ordered the creation of a crisis team to handle the accident, including top ministers and managed by the country's national security agency.

"We have prepared emergency planes to send to Tehran... to fly out the bodies of the victims, we are waiting a confirmation by Iran for their departure,"

Ukrainian Foreign Minister Vadym Prystaiko said that the victims were 82 Iranians, 63 Canadians, 11 Ukrainians including all the crew, 10 Swedes, four Afghans, three Britons and three Germans.

Ukraine International Airlines has suspended flights to Tehran indefinitely.