The top spokesman for the U.S. military in Iraq says four American helicopters that crashed in the past couple of weeks were shot down. VOA's Jim Randle reports, the losses are prompting some changes in the way these aircraft are used.

Major General William Caldwell (3 Jan 2007 photo)

Major General William Caldwell, said for the first time, that a rash of recent helicopter crashes were caused by enemy action.

"It does appear that they were all the result of some kind of anti-Iraqi ground fire that did bring those helicopters down," said General Caldwell.

Twenty one U.S. military personnel and private security contractors died in the crashes.

"There has been an ongoing effort ever since we have been here, to target our helicopters," he said. "Obviously, based on what we have seen, we are already making adjustments in our tactics and techniques and procedures as to how we employ our helicopters in support of Iraqi security forces and coalition forces. We are making those appropriate changes."

Smoke billows from the site of an explosion in central Baghdad late 03 Feb 2007

The latest incident was Friday when a helicopter went down about 20 kilometers north of Baghdad, killing two U.S. soldiers.

Sectarian violence continued Sunday in Iraq, as police say bombings and shootings killed a number of people across the country.

Several policemen died in a roadside bombing in a Sunni area of northern Baghdad, and a car bomb killed several people and wounded more at a Baghdad bus station.

Those attacks came one day after a truck bomb attack killed more than 130 people at a market in a mainly Shi'ite district of Baghdad.

When a crowd gathered Sunday at the scene of the bombing to search for traces of their loved ones, police, worried about another possible attack, fired into the air to disperse the people.

Saturday's devastating blast was the fifth major bombing in less than a month targeting predominantly Shi'ite districts in Baghdad and the southern Shi'ite city of Hillah. It was one of the deadliest attacks since the war began.