SEYNE, France (AFP, REUTERS) - French President Francois Hollande, German Chancellor Angela Merkel and Spain's Prime Minister Mariano Rajoy arrived near the site of the crashed Germanwings Airbus A320 airliner on Wednesday.

The three leaders met rescue workers and police at the crisis centre set up in the wake of the previous day's air disaster in which 150 people were killed.

Investigators tried to discover what had caused the first major air disaster in France in 15 years, but Lufthansa said on Wednesday it could not explain why the Airbus had crashed.

Investigators said the remoteness of the crash site meant it could be days before a clear picture emerged of Tuesday's tragedy.

However they said the fact that debris was restricted to a small area showed the A320 was not likely to have exploded in mid-air, suggesting a terrorist attack was not to blame.

"It is inexplicable this could happen to a plane free of technical problems and with an experienced, Lufthansa-trained pilot," Lufthansa chief executive Carsten Spohr told reporters in Frankfurt.

Germanwings executive Thomas Winkelmann said the company was still working on establishing the countries of origin for all the victims, a task complicated by the fact that some passengers had dual nationality.

The airline had, thus far, counted two victims each from Australia, Argentina, Iran, Venezuela and the United States.

Britain, the Netherlands, Colombia, Mexico, Japan, Denmark, Belgium and Israel each lost at least one of their nationals, Mr Winkelmann said.

The airline said it had established contact with the families of 123 victims and offered grief counselling to them and was working with the German foreign ministry to reach relatives of the last 27.