By Jack Kim and Lisa Barrington SEOUL (Reuters) -Both engines of the Jeju Air plane that crashed last month contained duck remains, according to a preliminary report on Monday, with authorities still trying to determine what caused the deadliest air disaster on South Korean soil.

The first report on last month's Jeju Air crash in South Korea 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.