The U.S. military confirmed on Wednesday that a CH-46 helicopter went down northwest of Baghdad, but casualties were still unknown.

On Sunday, the U.S. military said that four U.S. helicopters that had crashed since Jan. 20 were shot down by "some kind of anti-Iraqi ground fire."

The following is the list of U.S. helicopters that had crashed since the Iraq war broke out in March, 2003.

2007:

-- On Feb. 2, a U.S. military helicopter crashed north of Baghdad, killing two soldiers.

-- On Jan. 28, a U.S. military helicopter crashed in a combat operation near southern Iraqi city of Najaf, killing two U.S. soldiers aboard.

-- On Jan. 23, a U.S. helicopter belonging to the American Blackwater private security company was shot down in central Baghdad and five civilian contractors aboard were killed.

-- On Jan. 20, a U.S. Blackhawk helicopter went down northeast of Baghdad, killing 12 people abroad.

2006:

-- On Aug. 8, a U.S. Marine helicopter carrying six crew members crashed in Anbar, west of Baghdad. Two crew were missing.

-- On May 14, a U.S. helicopter was shot down during clashes near Yusifiya. Two soldiers were killed.

-- On April 1, an AH-64D Apache Longbow helicopter crashed due to possible hostile fire west of Yusifiya, 15 km south of Baghdad.The two pilots were killed.

-- On Jan. 16, both crew members were killed when their Apache attack helicopter was shot down by a missile near Taji, north of Baghdad.

-- On Jan. 8, a UH-60 Black Hawk crashed near Mosul, killing all 12 on aboard which included eight service personnel and four civilians.

2005:

-- On Nov. 2, an AH-1 Super Cobra helicopter crashed, killing the two Marine crewmen.

-- On Jan. 26, a U.S. CH-53E Super Stallion transport helicopter crashed near the Jordanian border in western Iraq's Anbar province, killing 31 American servicemen, which is the deadliest single loss for U.S. troops since the war started.

2004:

-- On Jan. 8, a total of nine U.S. soldiers were killed when a UH-60 Blackhawk helicopter was forced to make an emergency landing near the volatile Iraqi town of Fallujah.

2003:

-- On Nov. 15, a total of 17 soldiers were killed when two UH-60 Blackhawks crashed near Mosul in northern Iraq.

Source: Xinhua