(Adds background) BAGHDAD, April 15 (Reuters) - Two U.S. military helicopters crashed north of Baghdad on Sunday, killing two soldiers and injuring five, the U.S. military said. In a statement, the U.S. military said it appeared the incident was caused by a mid-air collision and not an insurgent attack. The military gave no information on the type of helicopters involved in the crash near a large U.S. air base in Taji and said an investigation was under way. Insurgents shot down eight helicopters during a month-long period earlier this year, killing 28 people, mainly American soldiers. Six of those aircraft were U.S. military helicopters and the other two belonged to a private American security company.
