Marine Le Pen's nationalistic Eurosceptic party faced losses in big target cities, including Marseille and Toulon, although an ally, Eric Ciotti, who heads his own staunchly conservative UDR party, won in Nice, France's fifth-largest city.

The municipal elections were a test of both the depth of the far right's support base and the resilience of mainstream parties in France's fragmented political landscape, a year ahead of the presidential elections.

Opinion polls project that both Le Pen and her young protégé Jordan Bardella would perform strongly in the 2027 race. Le Pen is awaiting a ruling in her appeal against an embezzlement conviction before deciding whether she will run for a fourth time.

The 35,000 separate municipal ballots usually focus on local issues, and their outcomes do not provide a clear forecast of French President Emmanuel Macron's potential successor. However, they do show trends in popularity and in the type of possible alliances that can be struck.

Senior RN officials rejected suggestions that the party's defeat in Toulon showed that it had hit a 'glass ceiling' ahead of the presidential election, saying it had won dozens of local constituencies where it previously had no presence.

'The National Rally and its candidates have achieved tonight, in this municipal election, the biggest breakthrough in its entire history,' RN chief Bardella said.

His anti-immigration party held onto the southern city of Perpignan and won in other towns such as Menton and Carcassonne, also in the South. But the RN's failure to win larger cities, and in particular in Marseille, its most coveted prize, may show limits to its growing popularity.

Senior politicians on the mainstream right said the municipal elections showed they needed to be united to win - especially in next year's presidential election.

Former Prime Minister Edouard Philippe was re-elected mayor in his port city of Le Havre, in a boost to his hopes of running for president in 2027.

In Paris, Socialist Party candidate Emmanuel Gregoire fended off a challenge from conservative former minister Rachida Dati and ensured the French capital remains in left-wing hands.

In the second-biggest city, Marseille, the incumbent, Socialist Mayor Benoit Payan, was re-elected with 54% of the votes. He had been neck-and-neck with the RN in the first round, and was boosted after his hard-left rival pulled out of the run-off to prevent a far-right victory.

With wins in Paris and Marseille, the Socialist Party, long weakened nationally, has seen reasons for hope.

The Socialist Party said it had also beaten Francois Bayrou, a centre-right former prime minister of Macron, in the city of Pau.

The hard-left France Unbowed (LFI) won in the northern city of Roubaix, a city of nearly 100,000, and in the Saint-Denis suburb of Paris. The party put forward its highest number of candidates in local elections.

(With inputs from Reuters)