(Adds military spokesman on cause of incident) BAGHDAD, Feb 21 (Reuters) - A U.S. Black Hawk helicopter that went down north of Baghdad on Wednesday is believed to have been shot down, the military said. A statement from the U.S. military said all nine people on board were evacuated and there were no serious injuries. "The indications are now, again it's preliminary, but the indications are now that it was brought down by small arms fire and RPGs -- rocket propelled grenades," said Major-General William Caldwell, the chief U.S. military spokesman in Iraq. "It did land safely. All nine occupants were transferred to another helicopter," he told CNN. Before Wednesday's incident, insurgents had shot down seven helicopters in Iraq since Jan. 20, killing 28 people, mainly American soldiers. Five of those helicopters were U.S. military aircraft and two belonged to an American security company. The incidents have raised questions about whether insurgents are using new tactics, such as studying aircraft flight patterns, or have acquired sophisticated weaponry. U.S. commanders have said one reason they believe insurgents had focused on helicopters was to try to undermine a security crackdown in Baghdad that began last week. Iraqi police captain Mahmoud al-Mashhadani said he saw some type of projectile hitting the helicopter before it came down in a rural area known as the Line, 30 km north of Baghdad. "I saw a ball of fire hitting the aircraft and smoke coming out of the helicopter as it came down," Mashhadani told Reuters.
