HONOLULU — All six Marines killed in the crash of a U.S. helicopter in Afghanistan were based in Hawaii, a Hawaii congresswoman said Friday.

The CH-53D helicopter crashed Thursday in Afghanistan's southern province of Helmand.

U.S. Rep. Colleen Hanabusa, a member of the House Armed Services Committee, said Friday she's saddened to hear of the deaths. Her spokeswoman, Ashley Nagaoka Boylan, said the congresswoman was notified Thursday evening that all six Marines were Hawaii-based.

"All who have called Hawaii home are part of our island ohana, and every loss like this touches us deeply," Hanabusa said in a statement, using the Hawaiian word for family.

A senior U.S. defense official confirmed all six were Marines on condition of anonymity because the U.S. command in Afghanistan had not yet publicly released details.

The Vietnam War-era helicopter is the same model as one that crashed and killed a Marine in a bay off Hawaii on March 29. An investigation later revealed mechanical failure caused that accident.

The defense official said there is no indication that the helicopter in Afghanistan was hit by enemy fire.

Chuck Little, spokesman for Marine Forces Pacific at Camp Smith on Oahu, said he could not provide information about the crash.

Thursday's crash was the deadliest in Afghanistan since August, when 30 American troops died after a Chinook helicopter was apparently shot down in Wardak province in the center of the country.

The cause of the latest crash is still being investigated, but a statement issued by the NATO international military coalition said there was no enemy activity in the area when it happened.

German Brig. Gen. Carsten Jacobson, a spokesman for the NATO coalition in Kabul, said officials were looking at a "technical fault" as the possible culprit.

"The helicopter is one of the safest forms of transport," Jacobson said. He said not only does it protect troops the danger of roadside bombs on the ground, but it is well-tested, well-proven way to travel.

CH-53D Sea Stallion helicopters were first used in the 1960s, and the Marine Corps used them in the Vietnam War.

All Sea Stallions still used operationally are stationed at Marine Corps Base Hawaii in Kaneohe Bay. The military plans to replace them with the MV-22 Osprey.

"The loss of the six U.S. Marines in yesterday's helicopter crash in Afghanistan comes as tragic news for our island community and our nation," U.S. Rep. Mazie K. Hirono, of Hawaii, said in a statement. "We owe them and all of our brave servicemen and women a debt of gratitude for their dedication to our country."

AP National Security Writer Robert Burns in Washington contributed to this report.