Updated

The French prosecutor's office has opened a preliminary investigation after a press report alleged that a police intelligence note had been post-dated to cover up a failure to act against an Islamic extremist who ultimately slit the throat of a Normandy priest.

A judicial official said on Friday the probe concerns charges of forgery and alteration of documents. The official said the decision to investigate was triggered by a complaint filed by civil parties in the 2016 case surrounding the murder of the priest by two extremists. The official wasn't authorized to speak publicly and couldn't be named.

The online investigative publication Mediapart revealed on Thursday the existence of the intelligence note.

A statement by the Paris police chief denied the note raised the possibility of an attack.