Hassan Rezaeifer, the head of accident investigations for the civil aviation department, said it was not possible to read the black boxes in Iran, without elaborating. He said French, American and Canadian experts would help analyze them in Kyiv, the Ukrainian capital.

He said if that doesn't work the black boxes will be sent to France. His remarks were carried by the semi-official Tasnim news agency.

Iran's Revolutionary Guard accidentally shot the plane down shortly after it took off from Tehran on Jan. 8, killing all 176 people on board. Hours earlier, the Guard had launched ballistic missiles at U.S. troops in Iraq in response to the U.S. airstrike that killed Iran's top commander, Gen. Qassem Soleimani. Officials say lower-level officers mistook the plane for a U.S. cruise missile.

Iranian officials initially said the crash was caused by a technical problem and invited countries that lost citizens to help investigate. Three days later, Iran admitted responsibility after Western leaders said there was strong evidence the plane was hit by a surface-to-air missile.

The victims included 57 Canadian citizens as well as 11 Ukrainians, 17 people from Sweden, four Afghans and four British citizens. Most of those killed were Iranians. The other five nations have demanded Iran accept full responsibility and pay compensation to the victims' families.

The plane was a Boeing 737-800 that was designed and built in the U.S. The plane's engine was designed by CFM International, a joint company between French group Safran and U.S. group GE Aviation. Investigators from both countries have been invited to take part in the probe.