Lufthansa says that cleanup workers have removed 80 percent of the debris from the site of a plane crash last month in the Alps that killed 150 people.

Lufthansa representative Carsten Hernig said Wednesday that cleanup teams had cleared 35 tons of waste as of Tuesday. Hernig is overseeing the operation to recover pieces of the shattered plane, operated by Lufthansa's low-cost carrier Germanwings.

He said workers will ensure that the debris, including 4 tons of kerosene and 90 liters of lubricants, are cleared safely and without leaving environmental damage to the Alpine mountainside. Hernig spoke to reporters alongside French officials in the town of Digne-les-Bains.

Prosecutors believe that the co-pilot of Flight 9525 intentionally crashed the Barcelona-Duesseldorf flight March 24 and are trying to determine why.