The killing of a policeman and his partner near Paris on Monday night was a "terrorist attack", a French government spokesman has said.
Islamic State's Amaq news agency said one of the group's fighters was responsible for the killing.
Flooding that has wreaked havoc in parts of France could cost between £700 million and £1.1 billion, the French Insurance Association warned.
So far, hundreds of towns and villages have been hit by flooding across the country.
Four people were killed during the adverse weather that left areas inundated near the Seine and Loire rivers.
Paris's biggest museums, the Louvre and Musee d'Orsay, were even forced to close as the Seine climbed to 6.1 metres (20ft) on Friday night, its highest level since 1982.
Now the FIA has warned damage costs would spiral into the billions.
As of Monday, 14 departments remain on alert in parts of Normandy, Paris and the Loire, while 7,000 properties are still without power.
French soldiers are standing guard outside the largest mosque in Paris following earlier reports of planned terror attacks in the country.
ITV News' Security Editor Rohit Kachroo said the Grand Mosque of Paris was not a target being investigated by the French.
But it's more than a fortnight since the terror suspect's arrest in Ukraine - so this more an act of reassurance
It comes after it was revealed a 25-year-old Frenchman was arrested last month on the Ukrainian-Polish border on suspicion of plotting mass attacks during Euro 2016.
The water level of the Seine river in Paris is finally falling after it reached its peak overnight, the highest in 35 years.
Floods across France, Germany, and Belgium in recent days have seen at least 11 people killed, with thousands evacuated and many more left without power.
French authorities have warned that it could take 10 days for the river to return to its normal level after flooding swelled it to 15 feet (4.5m) above average in Paris.
More than 17,000 homes were still without electricity on Saturday in the Paris region and centre of France.
Authorities have also shut the Louvre museum, the national library, the Orsay museum and the Grand Palais, Paris' striking glass-and-steel topped exhibition centre.
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A Frenchman has been arrested in Spain on suspicion of supplying the weapons that were used to kill five people at a kosher deli in Paris last year.
The 27-year-old man is from Sainte Catherine and was arrested in the Malaga area on Tuesday, in a joint operation with French police, Spain's interior ministry said in a statement.
Amedy Coulibaly shot dead a police officer and four hostages in the supermarket in January 2015, a day after two other gunmen killed 12 people in an attack on the Charlie Hebdo newspaper office in Paris.