Iran may request assistance in deciphering the "black boxes" of the Boeing 737-800 airliner that crashed near Tehran. Russia, Ukraine, France and Canada may be asked for assistance, Bloomberg said referring to a statement of Hassan Rezaifar, the head of Iran's Civil Aviation Organization commission for accidents investigation from Iran's flight regulator.

Iran is confident that the Ukrainian plane was not shot down by a missile.

Rezaifar said on Friday experts would try to inspect the "black boxes" in order to understand whether it is still possible to extract information from them.

Iran does not want black boxes to be exported outside the country for analysis. Three Iranian airlines, he said, will help experts with their study.

He added that an investigation into a plane crash could take from one to two years.

At the same time, Rezaifar, commenting on videos posted to the Internet purporting to show missiles hitting the airplane, said the video clips need to be checked.

Earlier, the Associated Press reported that, to participate in the investigation of the causes of the crash, the Iranian authorities invited the U.S. National Transportation Safety Board to participate in the investigation of the crash. The board said it would "assess the level of its participation in the investigation."

However, the agency notes that the level of participation of the council in the investigation may be limited due to U.S. sanctions against Iran. However, the board may become involved in the investigation, because the airplane that crashed was built in the United States.

On Thursday, Canadian Prime Minister Justin Trudeau said intelligence agencies of Canada and its allies believe that the cause of the crash of theUkrainian passenger plane near Tehran was a surface-to-air missile.

"We have intelligence from many sources, including from our own intelligence services and from the intelligence of our allies, according to which the plane was shot down by an Iranian ground-to-air missile," said Trudeau, quoted by Canadian television.

The UIA Boeing 737-800 passenger plane, flight PS752 from the Tehran to Kyiv, crashed in the area of Imam Khomeini International Airport in Tehran immediately after take-off early on the morning of January 8. Some 167 passengers and nine crew members on board died.

Among the dead were 11 citizens of Ukraine (among them 9 crew members), 82 citizens of Iran, 63 – of Canada, 10 – of Sweden, four – of Afghanistan and three each from Germany and the UK.