LOS ANGELES, Sept 1 (Reuters) - A search for six coal miners trapped in the Crandall Canyon Mine in Utah is over after 25 days, an official with the U.S. Mine Safety and Health Administration said on Saturday.

"Unfortunately, our hopeful efforts have resulted in no signs of life from these miners," Richard Stickler, assistant secretary for MSHA, said in a statement.

"Sadly, there is no remaining hope of finding these miners alive."

The six have not been heard from since the mine in Huntington, Utah, collapsed on Aug. 6, stranding them some 1,800 feet (550 metres) below ground.

It remains unclear what caused the collapse. Mine co-owner Robert Murray has said it was triggered by an earthquake but geologists disagree, saying the collapse caused magnitude 3.9 seismic waves.

Below-ground search efforts for the trapped miners were suspended after three rescuers were killed and six injured by a cave-in on Aug. 16.

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