Jan. 8 (UPI) -- Investigators have located the "black boxes" from a Ukrainian airliner that crashed in Iran Wednesday and killed all 176 people aboard, state media reported.
Broadcaster IRIB said the flight data and cockpit voice recorders were found at the crash site near Parand, about 35 miles southwest of Tehran. The Boeing 737 went down shortly after it left Imam Khomeini International Airport.
The head of Iran's civil aviation authority said Tehran would not give the recorders to U.S.-based Boeing, Iran's semiofficial news agency Mehr reported.
The flight crashed with 167 passengers and nine crew aboard.
"Unfortunately, all the passengers died," Pir-Hossein Koulivand, Iran's Emergency Medical Service chief, said.
Among the dead were 82 Iranians, 63 Canadians, 11 Ukrainians, 10 Swedes, four Afghans, three Germans and three Britons, Ukraine's Foreign Minister Vadym Prystaiko said in a tweet.
Ukraine President Volodymyr Zelensky said in a Facebook post he would cut short a visit in Oman and return to Kiev.
Ali Khashani, a senior official at Imam Khomeini International Airport, said the crash was likely the result of a technical failure. The Ukrainian Embassy in Tehran initially agreed with that assessment, ruling out the possibility of an attack, but subsequently said it could not rule out any potential cause and deferred to an official commission to investigate.
Meanwhile, United International Airlines said it uses the Tehran airport to train on Boeing 737s and the crash was most probably not the result of the crew's error.
"Given the crew's experience, error probability is minimal," UIA Vice President Operations Ihor Sosnovsky said in a statement. "We do not even consider such a chance."
Ukrainian Prime Minister Oleksiy Honcharuk said in a statement an operational headquarters has been set up to investigate and Iranian consulate officials were at the site.
Zelensky declared Thursday a day of mourning, ordering all flags to be lowered and concerts and other entertainment performances to be banned.
"On behalf of all Canadians, I want to express my deepest condolences to those who are mourning the loss of a loved one. Your loss is indescribable, this is a heartbreaking tragedy. While no words will erase your pain, I want you to know an entire country is with you, we share your grief," he said.
Canada will work with its partners to "thoroughly" investigate the incident and it would not rule out any possible cause of the crash, he said.
"Canadians have questions," he said. "And they deserve answers."
Boeing said it was gathering information about the crash.
The crash is the latest blemish for the U.S. aviation giant, which will install new President and CEO David Calhoun on Monday to succeed Dennis Muilenburg, who was dismissed last month amid ongoing fallout related to trouble with Boeing's 737 Max fleet, which has been grounded worldwide for nearly a year.
Boeing has absorbed significant financial losses and damage to its reputation since two 737 Max 8s crashed in Indonesia and Ethiopia and killed nearly 350 people.