Meanwhile, two US military helicopters crashed north of Baghdad, killing two soldiers and injuring five, the US military said.
In a statement, the US military said it appeared the incident was caused by a mid-air collision and not an attack.
The military gave no information on the type of helicopters involved in the crash near a large US air base in Taji and said an investigation was under way.
Fighters shot down eight helicopters during a month-long period earlier this year, killing 28 people, mainly American soldiers. Six of those aircraft were US military helicopters and the other two belonged to a private American security company.