The Hotel Lambert mansion in central Paris, a 17th-century architectural jewel with a rich history, was damaged in a major fire on Wednesday amid controversial renovations after its purchase by the Qatari royal family.
Dozens of firefighters fought the blaze for about six hours after it broke out around 1:30 am (2330 GMT Tuesday) at the Lambert, a 'hotel particulier' or private townhouse, on Ile Saint-Louis overlooking the Seine.
Firefighters said the blaze started on the roof of the building, which was bought by Qatar's royal family from the Rothschild banking dynasty for some 60 million euros ($85 million) in 2007.
The fire "spread pretty fast because the building is empty and in the midst of renovation", fire service Lieutenant-Colonel Pascal Le Testu told AFP. "The operation was complicated because the structure is fragile," he said.
"Now we have to see how badly the structures were affected, as well as the state of the artworks inside that may have been reached by smoke and flames, but also water, despite our utmost efforts to protect them," he added.
Around a dozen neighbours were evacuated and one firefighter was slightly injured.
Built in the 1640s at the eastern tip of Ile Saint-Louis, the mansion was designed for a wealthy financier, Nicolas Lambert, by the architect Louis Vau, who went on to oversee an expansion of the Chateau de Versailles for Louis XIV.
The mansion is considered one of the finest examples of mid-17th-century French architecture, featuring frescoes by Charles Le Brun in the "Gallery of Hercules" and works by other masters of the day.
It is part of a World Heritage site along the banks of the Seine.
The mansion's uses over the years have included being a hideaway for 18th-century philosopher Voltaire and his lover, and a political headquarters for Polish exiles in the following century.
Its acquisition by the Qatari royal family, which enjoys strong diplomatic ties with France, sparked a dispute as heritage activists feared they would destroy a cultural gem.
Plans for large-scale renovations, including the installation of a parking area and vehicle lift, were initially blocked by a French court following complaints from activists and neighbours.
Supporters of the Qatari family's plans said the mansion had been neglected and damaged over the centuries and was in desperate need of repairs. Some also suggested the criticism was rooted in opposition to seeing foreigners buy exclusive properties in rarefied central Paris.
The dispute was finally resolved in January 2010 when an agreement was signed with a heritage association after weeks of delicate government-supervised negotiations.
Now the fire has raised concerns that historic parts of the building have been destroyed anyway.
"It really is a catastrophe because we fought for the frescos of the Gallery of Hercules to be preserved in the renovation project and now everything has gone up in smoke or been drowned," said neighbour Sophie Pons.
Qatar's royal family has become a major investor in France, buying up prestige properties, investing in flagship companies such as energy giant Total and media group Vivendi, and purchasing football club Paris Saint-Germain.
The French foreign ministry estimates that Qatar has invested at least $15 billion (12 billion euros) in France over the last five years.