Video of final seconds aboard Germanwings plane discovered

Lufthansa is facing legal action from relatives of the victims.

Chief Executive Carsten Spohr, visiting the crash site on Wednesday, declined to answer a barrage of questions about what the airline knew of Lubitz' mental health.

Lubitz, who was allowed to restart training after passing all the medical and suitability checks again, had a note on his flight licence indicating some sort of illness, a person familiar with the matter told Reuters.

But under German doctor-patient confidentiality laws, Lufthansa as an employer may not seek information about employees' medical conditions.

Spohr said in a prepared statement that it was still not clear what drove Lubitz' actions.

The head of the French police forensic team said earlier this week it would take two to four months to identify the victims, and that there was no certainty all of them would be identified because of the high speed at which the plane crashed.

A first step could be just days away though, said Brice Robin, the Marseille prosecutor in charge of the case.

"We haven't yet isolated all 150 DNA sets but we hope to by the end of the week," he told Reuters.

"Then they need to be compared with those of members of the families of the victims, which will take a certain time."