The judge investigating last month's deadly train crash in northwestern Spain plans to question the officials responsible for railway safety as possible defendants.

Subpoenas will be issued once state-owned Adif provides the names of the personnel involved, Judge Luis Alaez said in an order issued Tuesday.

A high-speed train went off the rails on July 24 near Santiago de Compostela, killing 79 people and leaving more than 150 others injured.

While the crash was "obviously connected" with the actions of driver Francisco Jose Garzon, who has admitted the train was moving at double the 80 kph (49 mph) speed limit, the circumstances suggest that the rail safety measures may also have been inadequate, the judge wrote.

Garzon has been charged with 79 counts of negligent homicide.

The officials in charge of the stretch of track where the disaster took place should have implemented measures to prevent or ameliorate "foreseeable" human errors, Alaez said.

The crash on the outskirts of Santiago de Compostela was the second-worst rail accident in Spain's history. EFE