A church volunteer has been charged after he told investigators that he was responsible for an arson attack that badly damaged a 15th-century Gothic cathedral in western France.

The man had previously been questioned and then released after the blaze which destroyed the organ, shattered stained glass windows, and blackened the insides of the Cathedral of St Peter and St Paul in Nantes on July 18.

When he was detained again this weekend for further questioning, he finally admitted responsibility for the fire, said his lawyer, Quentin Chabert.

"He confessed to the allegations against him which, as the prosecutor indicated, are causing destruction and damage by fire," the lawyer told France Info radio.

"He regrets the facts. That is certain. He is in a sort of repentance."

French media quoted the Nantes prosecutor as saying that the 39-year-old Rwandan, who had been tasked with the job of locking up the cathedral, told the investigating magistrate that he lit three fires - on two cathedral organs and an electrical box. His motives were unknown.

The reports quoted the prosecutor as saying that the arson charge is punishable by a 10-year jail term.