The U.S. military helicopter that crash landed aboard a ship off Okinawa on Wednesday may have touched a crane on the vessel before the incident, Japanese government sources said Thursday.

Seven of the 17 crew members aboard the U.S. Army H-60 were injured in the crash landing, which occurred during a special forces drill to seize a hijacked ship, the sources said. Two of the injured were members of the Japanese Ground Self-Defense Force specializing in responding to terrorism and guerilla attacks, they said.

The U.S. military had initially said six crew members were injured but corrected the number to seven Thursday.