PARIS — Paris police investigators think an electrical short-circuit most likely caused the fire at Notre Dame Cathedral, a police official said Thursday, as France paid a daylong tribute to the firefighters who saved the world-renowned landmark.

A judicial police official told The Associated Press that investigators made an initial assessment of the cathedral Wednesday but don't have a green light to search Notre Dame's charred interior because of ongoing safety hazards.

The cathedral's fragile walls were being shored up with wooden planks, said the official, who spoke on condition of anonymity because he wasn't authorized to speak by name about an ongoing investigation.

Investigators so far believe the fire was accidental, and are questioning both cathedral staff and workers who were carrying out renovations. Some 40 people had been questioned by Thursday, according to the Paris prosecutor's office.

The police official would not comment on an unsourced report in Le Parisian newspaper that investigators are looking at whether the fire could have been linked to a computer glitch or the temporary elevators used in the renovation work, among other things. The prosecutor's office said only that "all leads must be explored".

AP