The Super Puma crashed at around midday on Thursday near the hospice on the remote mountain pass, killing both pilots.
“At this stage in the investigation we can say that a collision with a power cable caused the crash,” said investigator Tobias Kühne, according to a report in the Blick tabloid.
A power cable came down in the accident but it was not initially known whether this had caused the crash or happened as a result of it.
An analysis of the black box and voice recorders is expected to shed light on the reason why the two pilots, aged 50 and 39, were flying in the path of the cable.
The area is known for the high density of power cables, which can prove a hazard for pilots.
A flight assistant was injured in the crash, which happened just after the helicopter’s passengers – including four French military inspectors – had been dropped off on the ground.
On Thursday the Swiss defence military said in a statement all Super Puma flights had resumed after initial investigations confirmed that a technical fault was not to blame for the crash.
The crash was the latest in a series of accidents to affect the air force. Defence minister Guy Parmelin told the SonntagsBlick that despite this he still had full confidence in air force chief Aldo Schellenberger.
"I don't have any reason to dismiss him, he has not made any fundamental mistakes," Parmelin said.