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French authorities say they have no reason to believe that criminal action was to blame for a fire that tore through the iconic Notre-Dame cathedral in April.

The cause of the blaze remains unknown, but investigators are now probing the possibility of negligence.

A "badly stubbed out cigarette" or electrical fault are among the possible causes being considered.

The fire broke out at the Gothic landmark on 15 April, gutting its roof.

A statement, signed by the chief prosecutor of Paris, Remy Heitz, said no evidence had been found to suggest any "criminal origin" to the fire.

"The investigations carried out to this date have not yet been able to determine the causes of the fire," the statement said.

It added that "deeper investigations" would now be undertaken to find out if it had been a case of involuntary damage caused by negligence.

The fire at the famous French landmark shocked people around the world in April.

The 850-year-old building's spire and roof collapsed in the fire but the main structure, including its two bell towers, was saved.

Notre-Dame was undergoing restoration work at the time of the blaze.

Hundreds of millions of pounds have since been donated to restore the beloved cathedral, which draws an estimated 13 million visitors each year. The landmark has also played a role in key moments of French history, is seen as a major symbol of the Catholic faith and was the inspiration for the popular 1831 novel The Hunchback of Notre-Dame.

French President Emmanuel Macron has described the fire as a "terrible tragedy" and set a goal of renovating the building within five years.