The French public prosecutor heading the investigation into the Germanwings airliner crash in the French Alps that killed 150 people earlier this week alleged at a news conference on Thursday that the crash was caused deliberately by the plane's co-pilot, identified as Andreas Lubitz, a 28-year-old German national.

Marseille prosecutor Brice Robin cited what he said was evidence from a voice recorder in the cockpit.

"At this moment, in light of investigation, the interpretation we can give at this time is that the co-pilot through voluntary abstention refused to open the door of the cockpit to the commander, and activated the button that commands the loss of altitude," Robin told reporters.

"You can hear human breathing in the cockpit up until the moment of impact," Robin continued. "The pilot was therefore alive."

According to Reuters:

The world's attention will now focus on the motivations of Lubitz, a German national who joined the budget carrier in September 2013 and had just 630 hours of flying time - compared with the 6,000 hours of the flight captain, named in German media only as "Patrick S." in accordance with usual practice.

Robin said there were no grounds to suspect that Lubitz was carrying out a terrorist attack. "Suicide" was also the wrong word to describe actions which killed so many other people, the prosecutor added: "I don't necessarily call it suicide when you have responsibility for 100 or so lives."

The prosecutor claimed the co-pilot did this "for a reason we do not know, but [it] can be seen as a willingness to destroy the aircraft."

The prosecutor's statements immediately followed news reports on Thursday that one of the co-pilots had been locked out of the cockpit.

A spokesman for Lufthansa, which owns Germanwings, said: “We have no information from the authorities that confirms this report and we are seeking more information. We will not take part in speculation on the causes of the crash.”

Meanwhile, families of the victims were being transported to Marseille on Thursday, before traveling to an area close to the site of the tragedy.

The crash killed people from the United States, Morocco, Britain, Argentina, Australia, Belgium, Colombia, Denmark, Israel, Japan, Mexico, Iran, and the Netherlands, according to officials.