An Iraqi army plane crashed during a reconnaissance flight near the city of Kirkuk on Wednesday and its three crew went missing, a high-ranking military source said, blaming a "technical problem".
The Islamic State jihadist group claimed it had shot down an Iraqi military plane in the area, killing five crew members.
The military source said authorities had launched a search for the crew after the Cessna 208 Caravan went down near Kirkuk, around 220 kilometres (135 miles) north of Baghdad.
In a statement on Twitter, IS said it had shot down a military plane with anti-aircraft artillery and that it been on a bombing run against the city of Hawija, a stronghold of the jihadists in Kirkuk province.
Iraqi forces have been making gains against the jihadists in recent months as they seek to reclaim territory seized by IS during a major offensive in 2014.