Iran denied the reports that a missile had caused the crash, in which all 176 people aboard died when the plane went down soon after takeoff near Tehran on Wednesday.

"The circumstances of this catastrophe are still unclear," Ukrainian deputy foreign minister Sergiy Kyslytsya said at a UN meeting in New York.

"It's now up to experts to investigate and to find answers to the question of what caused the crash. To do so, our experts must receive unconditional support for their investigation."