Military officials said the Sea Knight CH-46 was on a routine mission, and initial reports indicated that the helicopter experienced mechanical problems. An Internet posting by the Islamic State in Iraq, an umbrella organization that encompasses militant groups such as al-Qaida in Iraq, claimed responsibility for attacking the helicopter.
"[T]he resistors ambushed one of the ... helicopters among the date palms and the citrus trees," part of the statement said. "And hundreds of people, at least, watched it burn and their voices shouted, 'God is great,' thanking God."
Soon after the helicopter crashed, U.S. Army forces sealed off the area and began investigating the plan of the attack.
According to the Associated Press, witnesses saw an anti-aircraft missile strike the helicopter between the Taji air base, around 20 miles northwest of the city.
The Islamic State in Iraq also has claimed responsibility for the four previous helicopter crashes, all of which were shot down with similar technology mentioned in the group's online statement, prompting U.S. officials to change their policy for helicopter operations.
In the earlier attacks, 16 U.S. soldiers and five private security officers were killed.
After the fourth helicopter attack, military spokesman Maj. Gen. William Caldwell said that the military is "already adjusting our tactics and procedures in how we deploy our helicopters."
In a congressional hearing held Tuesday, Gen. Peter Pace, the chairman of the Joint Chiefs of Staff, came under questioning about the recent string of attacks and whether they represented a buildup in armaments by insurgents.
"At this point and time, I do not know whether or not it is the law of averages that caught up with us or if there's been a change in tactics, techniques and procedures on the part of the enemy," said Pace.
Wednesday's attack occurred as Iraqi Prime Minister Nouri al-Maliki announced that the Iraqi military is behind schedule on implementing the security plan and that planned security crackdowns have not been progressing as fast as necessary.