*Ukraine's President Volodymyr Zelenskiy said the government was considering several possible causes of the plane crash

*January 9 is declared the day of national mourning in Ukraine

*As of now, there is no report of Chinese citizens on the plane

*The victims included 82 from Iran, 63 Canadians, 11 Ukrainians, 10 Swedes, 3 Germans and 3 Britons

*Iran's civil aviation authority has said it will not hand over two black boxes to the plane's manufacturer Boeing or the United States, but will cooperate with Ukraine

*Both of the plane's black box voice and data recorders had been found, Iranian state television reported

*Ukraine's embassy in Iran dropped an initial reference to engine failure as the cause of the plane crash outside Tehran

*US airplane giant Boeing Company said that it is ready to provide any necessary assistance after the Ukrainian airplane crash

*China expressed deep condolences to the victims of the Ukrainian Airlines plane crash

China on Wednesday expressed deep condolences to the victims of the Ukrainian Airlines plane crash and extended heartfelt sympathies to their families, according to a Foreign Ministry spokesperson.

Reports said that a Ukrainian Airlines passenger plane, with 176 people on board, crashed this morning near Iran's Imam Khomeini International Airport shortly after taking off. All passengers and crew were killed.

Spokesperson Geng Shuang said China hopes all relevant parties can ascertain the cause of the crash as soon as possible.

"The Chinese embassy and consulates in Ukraine have already contacted Ukrainian authorities to verify the situation," said Geng, adding that as of now, there is no report of Chinese citizens on the plane.

Ukraine International Airlines representatives have denied mistakes by the crew in the Boeing 737 crash which took the lives of 167 passengers and nine crew members on Wednesday.

"We have information that the plane climbed 2,400 meters in altitude. The chances of the crew making a mistake are minimal; we simply don't think so. It's hard to say that something was wrong with the crew given their experience," Igor Sosnovsky, vice president for flight operations of UIA, told a press conference held at Boryspil International Airport.

UIA President Yevhenii Dykhne said that the Boeing 737-800 plane went through scheduled maintenance on Monday before departure. The aircraft was built in 2016 and delivered directly to the airline from the manufacturer.

"We decided to cancel flights to Iran for a certain period (of time). The airline carries out all the international air traffic procedures," said the head of the company.

Ukraine's embassy in Iran, citing preliminary information, said the Boeing 737 suffered engine failure and the crash was not caused by "terrorism".

Carrier Ukraine International Airlines said it was doing everything possible to confirm the cause, and the investigation would also involve Boeing and Ukrainian and Iranian authorities. It was the Kiev-based airline's first fatal accident.

Ukraine President Volodymyr Zelenskiy said all on board had died. "My sincere condolences to the relatives and friends of all passengers and crew," he said in a statement.

"The fire is so heavy that we cannot do any rescue ... we have 22 ambulances, four bus ambulances and a helicopter at the site," Pirhossein Koulivand, head of Iran's emergency services, told Iranian state television.

Ukraine's prime minister and Iranian state TV said 167 passengers and nine crew were on board. 

Ukrainian Foreign Minister Vadym Prystaiko said the victims included 82 from Iran, 63 Canadians, 11 Ukrainians, 10 Swedes, three Germans and three Britons. Most passengers were in transit, the airline said.

Iranian media quoted a local aviation official as saying the pilot did not declare an emergency.

Iranian TV said the crash was due to unspecified technical problems. State broadcaster IRIB said on its website that one of the plane's two black boxes - the flight data recorder and the cockpit voice recorder - had been found.

GOOD SAFETY RECORD

The plane that crashed was a three-year-old Boeing 737-800NG en route to Kiev, air tracking service FlightRadar24 said.

"The last scheduled maintenance of the aircraft took place on 06 January, 2020," the airline said.

A spokesman for the manufacturer said it was gathering more information.

The 737-800 is one of the world's most-flown models with a good safety record and does not have the software feature implicated in crashes of the 737 MAX. Boeing grounded its 737 MAX fleet in March after two crashes that killed 346 people.

The 737-800's twin engines are made by CFM International, a US-French venture co-owned by General Electric and France's Safran.

Modern aircraft are designed and certified to cope with an engine failure shortly after take-off and to fly for extended periods on one engine. However, an uncontained engine failure releasing shrapnel can cause damage to other aircraft systems.

Under international rules overseen by the United Nations, Iran is responsible for leading the crash investigation.

Xinhua/Reuters