Black Hawk medivac helicopter (search), clearly marked with a red cross, crashed Thursday after a witness said it was hit by a rocket, killing all nine U.S. soldiers aboard. In Baghdad, a C-5 transport plane (search) with 63 passengers and crew limped safely back to the airport after being struck by fire from insurgents.

About 80 Iraqi prisoners, meanwhile, were released from Baghdad's Abu Ghraib prison, but they were not the detainees that U.S. authorities had promised would be freed under a special amnesty.

The military said a U.S. soldier died Wednesday of injuries suffered when a mortar attack that wounded 30 other troops and a civilian west of Baghdad (search).

The deaths brought to at least 495 the number of Americans killed in Iraq from hostile and non-hostile causes since the start of the war in March, according to the U.S. Central Command and the Department of Defense.

The Black Hawk went down about four miles south of Fallujah, a stronghold of the anti-American insurgency, the 82nd Airborne Division said.

The military said the cause of the crash was not known, but a witness, Mohammed Ahmed al-Jamali, said he heard the distinctive whoosh of a rocket and saw the helicopter, which was clearly marked with red crosses signifying its medical mission, struck in the tail.

The 27-year-old farmer who lives close to the crash site said he rushed to the scene but found everyone dead.

The helicopter was a medical evacuation aircraft but it was unclear if it was carrying patients, a military official said, speaking on condition of anonymity.

Another witness, student Waleed Kurdi, 23, said he heard "a loud explosion and I saw the fire in the air" as the chopper exploded in two before it hit the ground.

Twice before, American helicopters have gone down near Fallujah, a city 35 miles west of Baghdad.

A OH-58 Kiowa observation helicopter went down Jan. 2, killing one soldier. Military officials said it almost certainly was shot down. And on Nov. 2, a Chinook helicopter was shot down near the city, killing 16 American soldiers and injuring 26. The military believes a SA-7 shoulder-fired missile hit one of the chopper's rear-mounted engines.

In Thursday's close call at Baghdad International Airport, a transport plane carrying 63 people declared an in-flight emergency because of "excessive" vibrations in the No. 4 engine and landed safely shortly after takeoff, the Air Force said.

The Air Force later issued a brief statement saying initial information indicated the engine exploded as a result of "hostile action from the ground." The statement said no injuries were reported.

In November, a shoulder-fired missile struck a DHL cargo plane at the airport, forcing it to make an emergency landing at the airport with its wing aflame. All three crew members were unhurt.

Last month, guerrillas hit a C-17 transport plane with a surface-to-air missile shortly after it took off from Baghdad, causing the engine to explode. The plane returned to the airport and landed safely, with only one of the 16 people aboard slightly injured.

Wednesday's mortar attack occurred at Logistical Base Seitz about 12 miles west of Baghdad in the tense "Sunni Triangle" that is home to hard-line supporters of ousted leader Saddam Hussein.

The mortars hit "a living area where they have their sleeping quarters," a military spokesman said.

Seven of the wounded were treated and returned to duty and the others were hospitalized at the base, the military said. A statement said earlier reports of 33 wounded was a miscount by authorities.

At Abu Ghraib, the jail where Saddam Hussein's regime held and tortured its political opponents, hundreds of people waited in frustration for hours for the first of a group of detainees that coalition officials said would be freed as a goodwill gesture.

At one point, three truckloads of prisoners were driven out of the prison and those waiting rushed into the street after them, stopping traffic. An official said it was a routine release of about 80 prisoners that had nothing to do with the amnesty announced Wednesday by U.S. administrator L. Paul Bremer.

"These are the ones who are routinely released every week," said Lt. Col. Roy Shere, a spokesman for the 800th Military Police Brigade that operates prisons in Iraq.

Bremer had said 506 of some 12,800 detainees would be released and that the first 100 would be freed Thursday from Abu Ghraib. The rest were expected to be freed from camps all over the country in the coming weeks.

Bremer said that before they are released, the prisoners must first renounce violence and have a community or tribal leader take responsibility for them.

U.S. and coalition troops have rounded up thousands of people suspected of attacks or of funding the anti-American insurgency.

Relatives at the prison said people were being arrested unjustly.

Coalition officials said those to be released were low-level "associates" of insurgents and not directly involved in any attacks.