A U.S. helicopter on a humanitarian mission in the Philippines apparently was shot at, prompting the Navy to temporally halt the mission, a defense official said Monday.

An MH-60 helicopter operating from USNS Mercy hospital ship had gone to pick up 11 passengers about 50 miles (80 kilometers) inland, and two bullet holes were found when the aircraft returned to the ship with the passengers.

"The holes appear to be an entry and exit point from a single bullet," said Cmdr. Jeff A. Davis, a Navy spokesman.

It is unclear if the bullet struck while the passengers were on the helicopter, he said. There were no injuries and the aircraft's commander was unaware of any bullet striking the aircraft during the flight, Davis said.

The Mercy is anchored in Cotabato, conducting Pacific Partnership 08, a humanitarian civic assistance mission between nations — and with non-governmental organizations — to provide medical, dental, construction and other services ashore and afloat.

"The USNS Mercy mission commander has ceased all Mercy Pacific Partnership activities until a proper assessment can be made," Davis said in an e-mail.