A U.S. Army helicopter with 12 American military personnel on board has crashed into the sea in the Philippines. No survivors have been found.

A Pentagon spokesman says the crash occurred at night shortly after the Chinook helicopter took off from the southern island of Basilan where U.S. troops are training the Philippine military to hunt down Muslim rebels linked to the al-Qaida terrorist group.

The spokesman says there was no indication that the aircraft was brought down by hostile fire. He says another helicopter flying with it and additional aircraft searched the crash area but found no survivors.

The helicopter was on a routine transit mission. It was headed to an air base in the central Philippines that is being used as a staging base for the several hundred U.S. troops involved in the anti-terrorist training operation.