French firefighters battle a blaze at the Cathedral of Saint Pierre and Saint Paul in Nantes, France, July 18, 2020. (File photo: Agencies)

French police cleared a Rwandan refugee of all suspicion on Sunday and released him after questioning over a fire at the Nantes Cathedral.

The blaze tore through the cathedral in the northeastern city early on Saturday morning, destroying stained glass windows and the 400-year-old grand organ inside.

It took several hours to bring the fire under control, and the flames were completely extinguished by the afternoon. Most of the cathedral structure, built between the 15th and 19th centuries was saved.

The detained man, age 39, was a volunteer at the cathedral in charge of locking up the building the day before the fire.

The lawyer for the refugee, Quentin Chabert, said at the time of detention there was "nothing at this stage to link my client to the fire" and that the investigation must go on "with respect for everyone's rights and in particular those of my client".

The Nantes public prosecutor, Pierre Sennes, said the authorities had wanted to clear up any inconsistencies and that the questioning was a "normal procedure".

Authorities opened an investigation for suspected arson. Sennes said that three fires had been started at the site and there had been no signs of a break-in.

Jean-Charles Nowak, a clerk at the cathedral, told French newspaper Le Figaro the volunteer was "a man of duty" who had "suffered a lot in Rwanda" – a country he left several years ago. The refugee had been discussing extending his visa with local officials, he said.

"I don't believe for a second that he could have set the cathedral on fire. It's a place he adores," Nowak said.

The cathedral's rector, Hubert Campenois, said on Saturday that everything "was in order" on Friday evening and that "a very close inspection was made before it closed, like every evening".

Martin Morillon, president of the Nantes Cathedral association, described the loss of the organ as a "tragedy" that had left everyone "immensely sad".

"Disbelief is the predominant feeling today because it is our heritage that has disappeared, that has gone up in smoke," Morillon told LCI television. The fire comes a year after a blaze nearly destroyed Notre Dame Cathedral in Paris. Earlier this month, French President Emmanuel Macron announced its iconic spire would be rebuilt exactly as it was, ending speculation it would be changed to a more modern style.