BERLIN (REUTERS) - Lufthansa said on Wednesday it will take a long while to establish the events that led to the Germanwings plane crash last week.

"We are learning more every day about the causes of the accident," Chief Executive Carsten Spohr said in a statement on Wednesday near the crash site in France. "It will take a long long time for all of us to understand how this could happen."

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 Tuesday Lubitz had informed the flight school of a "severe period of depression" after taking a break in his pilot's training.