Lufthansa's Chief Executive Carsten Spohr said it will take a long while to establish the events that led to the Germanwings plane crash last week.

Spohr gave a statement to reporters on 1 April, after he and Germanwings managing director Thomas Winkelmann laid a wreath at the memorial erected in the tiny village of Le Vernet, near where the Germanwings plane came down on 24 March, killing all 150 people on board.

"It has now been one week after this terrible accident and our grief is still with us every day, everywhere and I think I speak for everybody in Lufthansa, that there is not a single hour when we don't think about this terrible accident, the victims, the relatives and friends of these victims. We are learning more every day about the cause of the accident, but I think it will take a long long time for everybody, all of us, to understand how this could happen," Spohr said.

"We are just very very sorry that such a terrible accident could have happened in Lufthansa, where we put so much focus on safety, we are sorry for the losses that occurred, and there are just no words to express this, and I try to express at least the words of thanks as I did today to those who have helped us here locally," he said.

He added that Lufthansa would support the local authorities to turn the crash site into a place of mourning and to restore the countryside when the investigation is finished.

He refused to answer questions on what Lufthansa knew about the mental health of Andreas Lubitz, who investigators believe deliberately crashed the plane.

Lufthansa said on 31 March that Lubitz had informed the flight school of a "severe period of depression" after taking a break in his pilot's training.