Authorities have suggested that migratory bird strikes were the cause of last month's deadly plane crash in South Korea, according to multiple reports.

The first report on last month’s Jeju Air crash in South Korea has confirmed traces of bird strikes in the plane’s engines, though officials haven’t determined the cause of the accident that killed all but two of the 181 people on board.

South Korea’s authorities investigating last month’s Jeju Air plane crash have submitted a preliminary accident report to the UN aviation agency and to the authorities of the United States, France and Thailand,