Iranian authorities found the black boxes of the crashed Ukrainian place, but said they won't turn them over to the U.S. authorities.

The Ukrainian Boeing 737 plane with 176 people from seven countries on board crashed in Tehran on Wednesday shortly after taking off, killing everyone on board.

A team of Ukraine experts were sent to Iran later on Wednesday to investigate the circumstances of the crashed airliner.

What happened?

Flight PS-752, a Boeing 737 Ukrainian International Airlines (UIA) passenger jet, crashed several minutes after taking off from Iran's Imam Khomeini Airport (IKA) in Tehran at 06:12 local time (02:42 GMT).

IKA spokesman Ali Kashani said the aircraft was carrying 167 passengers and nine crew members. 

Earlier reports said 180 people were on board.

The flight was bound for Kiev and most passengers were in transit and were due to connect to other flights on arrival in Ukraine, according to UIA.

The rescue operation was severely hampered by a huge fire at the site.

Iranian state television said the two black boxes have been discovered, and data could still reportedly be retrieved.

Who are the victims?

Ukrainian foreign ministry said the victims were:

82 Iranians

63 Canadians

11 Ukrainians

10 Swedes

4 Afghans

3 Germans

3 Britons

Ukraine Security Council earlier said nine crew members were among the 11 Ukrainian citizens killed in the crash.

What is the cause?

The cause of the crash has not been officially determined. The Ukrainian Embassy in Tehran initially ruled out terrorism or a missile attack, but later on withdrew its online statement and replaced it with another which said the causes had not been disclosed and that any previous comments were not official.

Meanwhile, Montana Khaledi, spokesman for Iran's Aviation Organization, said the crash was likely caused by technical failure.

However, UIA officials said during a press conference there was nothing wrong with its plane and that it was one of its best with excellent crew and very experienced pilots. The jet had its last scheduled maintenance on Monday.

UIA said it was suspending flights to Tehran indefinitely and vowed to find out the cause of the crash with a thorough investigation that will be conducted together with authorities from both Iran and Ukraine, as well as Boeing.

Ukrainian Foreign Minister Vadym Prystaiko and his Iranian counterpart Mohammad Javad Zarif have agreed to coordinate and create investigation groups to determine the cause.

Iran's aviation authority said it would not hand over the recovered black boxes to the U.S.

"We will not give the black boxes to the manufacturer (Boeing) and the Americans," Iran Civil Aviation Organisation head Ali Abedzadeh was quoted by Mehr news agency. 

"It's not yet clear which country the black box will go to for the investigation," he added. 

What are the responses?

Following the crash, Ukrainian President Volodymyr Zelensky cut a vacation in Oman short and flew back to Ukraine.

He also instructed his prosecutor general to open criminal proceedings and said a commission should be set up to investigate the causes of the crash.

Zelensky said the country will test the airworthiness of its entire civilian fleet of aircraft following Wednesday's crash.

He has also warned against speculation about the crash.

"I ask everyone to keep from speculating and putting forth unconfirmed theories about the crash," Zelensky wrote on Facebook.

China's Foreign Ministry expressed condolences to the families of the victims in the crash at its daily media briefing on Wednesday. 

Sweden's minister for foreign affairs Ann Linde conveyed condolences to her Ukrainian counterpart.

(With input from agencies)