As Ukrainians mourn more than 40 people who died in a plane crash in Iran on Monday, questions are being raised about what caused the crash.
Officials in Ukraine have declared Thursday a day of mourning for those who were on board a Ukrainian Antonov AN-140 plane when it crashed in Iran Monday evening.
Most of the passengers and crew on the flight to Iran were Ukrainians along with a few Russians. But Monday evening as the plane was preparing to land at an airport about 400 kilometers south of Tehran, it smashed into a mountain, killing all on board.
Officials in Iran have suggested that pilot error was to blame for the air disaster, but this drew a sharp response from the Ukrainian government. Ukrainian officials say the pilot was experienced and add that it is too soon to judge why the plane went down.
The passengers were on their way to Iran to take part in the test flight of a plane built in a joint-venture between Iran and Ukraine. Most of those on board were aviation experts.
The two countries are working together in Iran to produce locally-made versions of the Antonov AN-140 plane, the same type of plane that crashed on Monday. The locally-produced version is called the Iran-140.
Iranian officials have said they will go ahead with the planned test flight, but will hold a moment of silence for those who died.