Apo Island, Philippines ? A U.S. Army helicopter participating in anti-terrorism exercises with Philippine troops crashed into the sea early Friday with 10 Americans aboard, a U.S. official said. Three bodies were recovered.

The MH-47E Chinook helicopter appeared to be burning when it went down, witnesses said, but U.S. and Philippine officials say it was not hit by rebel fire. It was carrying eight crew and two passengers.

“We have found no survivors from the mishap aircraft,” said Brig. Gen. Donald Wurster, head of the U.S. contingent. “We, of course, hope they are alive and we are doing everything with our Philippine friends to find them.

“These were friends of mine, so it’s a difficult part of our jobs.”

The cause of the crash was unknown. Philippine military spokesman Lt. Col. Danilo Servando ruled out hostile fire.

Maj. Paul Fitzpatrick, an Army spokesman at Fort Campbell, Ky., said the eight-member crew was from the 160th Special Operations Aviation Regiment and that the other two men were Air Force para-rescue jumpers.

The 160th, known as the “Night Stalkers,” slips special forces commandos behind enemy lines aboard Black Hawk and Chinook helicopters.

Col. Alexander Aleo, commander of the Philippine military’s 103rd brigade headquarters on Basilan, said “everything looked normal” as the choppers dropped off the last of 160 U.S. special forces and supplies that have been arriving over the last two weeks to help the Philippine military.

Police said there was light rain and poor visibility at the time, but the chopper is equipped with advanced radar and other navigation gear.

“There was no indication of anything amiss before this thing happened,” Wurster said. “All we know is the helicopters were flying back on a routine transit mission when one of them crashed for unknown reasons.”

He said details of the incident remained sketchy.

Some debris and an oil slick were spotted five nautical miles from tiny Apo island in the Bohol Sea in the southern Philippines. Coast Guard Lt. Armand Balilo said one of the helicopter’s rotors had been found.

Officials said the turquoise water was believed to be more than 1,400 feet deep. As scuba divers searched the site, police combed the shore for debris, which residents said could have been carried several miles by swift currents.

Charito Tabanera, 37, said he was fishing off Apo when the helicopter crashed about two miles away.

“I saw a fireball and it fell into the sea,” he said.

Tabanera said the wind was so strong and the waters so choppy that he couldn’t head in the direction of the crash.

Fishing boat skippers Ricardo Zamora and Joel Lasola said they were about seven miles away when the helicopter went down.

“At the time of the incident, they saw a big fire that fell into the sea, and as the fire touched the water, there was an explosion,” said a police report based on their account.

Rodrigo Alanano, mayor of Dauin town on nearby Negros, said he talked with other fishermen who were about one or two miles from the crash site.

“They saw a helicopter in flames in the air, then it exploded as it fell into the sea,” he said. “They thought it was a meteorite.”

Later Friday, a U.S. military P-3 Orion maritime surveillance plane made an emergency landing at Mactan the MH-47E’s planned destination after one of its four engines developed problems, an official said. There were no reports of injuries or damage.

Some American and Philippine forces involved in the joint exercise were being pulled away to help.

“You can understand naturally that our hearts are full of sorrow right now,” said Maj. Cynthia Teramae, a U.S. spokesman. “What we are doing is focusing all our attention on the family members.”

She said the crash would not affect the exercise, which involves about 660 Americans including 160 special forces and targets the Muslim extremist Abu Sayyaf group. The rebels are holding a Kansas missionary couple and Filipino nurse hostage on southern Basilan island.

Rigoberto Tiglao, spokesman for President Gloria Macapagal Arroyo, said she expressed sympathy to the Americans’ families.

“This just goes to show that this support of the United States is not just any support,” Tiglao said. “They’re risking the lives of their own soldiers, too.”

Officials said the helicopter had finished three night flights between Zamboanga, home to the Philippine military’s Southern Command, and nearby Basilan, an Abu Sayyaf stronghold.

The ill-fated helicopter left Zamboanga with another chopper at 12:53 a.m. (11:53 a.m. EST) for a two-hour flight to Mactan, an islet near the city of Cebu where the United States has a supply base for the Basilan mission, Servando said.

Wurster said the first indication that something was amiss came at 2:34 a.m. (1:34 p.m. EST). Seven minutes later, two crewmen from the second helicopter jumped into the tropical waters to search, unsuccessfully, for survivors.

A U.S. Navy P-3 and a U.S. Air Force C-130 airplane rushed to the scene, as did Philippine aircraft and ships.

The Americans have been using extremely tight security, with transport planes landing at night with all of their lights off. Aleo said the two helicopters used a system in which one landed never turning off its engines while the other hovered above as a defensive measure.

“There was no mechanical trouble reported or any rebel activity that might have affected their flight,” Aleo said.

With its distinctive tandem rotors, the MH-47E is a special forces version of the CH-47 heavy transport helicopter that has been in use since 1962. The U.S. military is believed to have about 25 MH-47E choppers.