Four Marines Killed In Iraq Helicopter Crash

"There was no indication of hostile fire," said a defense official, who asked not to be identified.

The twin-engine Sea Knight aircraft came down in water near the city of Karbala, 68 miles (110 km) southwest of Baghdad, Pentagon sources said.

"At this point we believe the crew of four did not survive," a second defense official said.

"A fifth Marine observed the crash, went in to try to rescue them, and didn’t survive either," he said.

It was not immediately clear what happened to the fifth marine.

"We just have early reports. There are still a lot of questions," the official said.

The CH-46 has been in service since the 1960s, typically ferrying troops and equipment to and from the front line.