A U.S. transport helicopter crashed Tuesday near an air base west of Baghdad, killing five troops, the military said.
The CH-47 Chinook helicopter was conducting a routine post-maintenance test flight when it went down near Taqaddum air base, said 1st Lt. Shawn Mercer, a Marine spokesman.
He said emergency response crews had sealed off the site and the cause was still under investigation.
A military statement later said five American service members were killed in the crash.
The deaths raised to at least 3,700 members of the U.S. military who have died since the Iraq war started in March 2003, according to an Associated Press count.
The air base is about 70 kilometers (45 miles) west of Baghdad in restive Anbar province, a Sunni insurgent stronghold that has become calmer in recent months as tribal leaders have joined forces against al-Qaida in Iraq.
It was the deadliest helicopter crash in Iraq since Feb. 7, when a Marine CH-46 Sea Knight was shot down by insurgents, also in Anbar, killing all seven people on board.
That and a series of other helicopter downings earlier this year led U.S. officials to raise fears that militants were finding more sophisticated way to target American aircraft and the military began adjusting its tactics to fend them off.
The U.S. military relies heavily on helicopters to avoid the threat of ambushes and roadside bombs — the deadliest weapon in the militants’ arsenal. Any heightened dangers to aviation would be a serious challenge, especially as the Americans have boosted their forces in the Baghdad area as part of a new offensive.