Paris - -Greenpeace activists on Friday pulled off a daring stunt in central Paris, attaching a giant banner to the iconic Eiffel Tower and leaving police to admit security "flaws" at a time when terror fears remain high.
Though security has been increased around French tourism sites, the activists managed to hang from ropes and attach a 30m-long banner reading "Liberty, Equality, Fraternity" and "#resist" in protest at the programme of far-right presidential candidate Marine Le Pen.
The activists hung the banner from an arch connecting two legs of the iconic 324m Iron Lady, a symbol of Paris.
Twelve people were arrested over the Greenpeace stunt in which a safety net was also damaged and which came two days before France votes in a divisive second round of the presidential election.
Le Pen faces centrist Emmanuel Macron in Sunday's run-off. Polls give him a lead of 22-24 percentage points.
The incident revealed "flaws in the monument's security programme", Paris police said in a statement.
France is on high alert after a string of jihadist attacks in the past two years that have killed over 230 people.
The Paris city hall denounced the Greenpeace action.
"It is inadmissable that a monument like the Eiffel Tower, the emblem of Paris for Parisians and for all French people, should be used for political ends," the mayor's office said in a joint statement with the police.
As a consequence the police have decided to increase patrols around the Eiffel Tower along with security teams with dogs.
The numbers will also be boosted at the tower's supervision centre and the video surveillance system reviewed.
Paris officials announced in February plans to protect visitors by erecting bulletproof glass walls at the northern and southern ends of the monument area.
The glass walls are intended to prevent individuals or vehicles storming the site visited by six million people each year, making it the world's most visited paying monument.
Greenpeace France head Jean-Francois Julliard told reporters the protest was intended as "a warning against Marine Le Pen's programme and the dangers it poses for NGOs and others."
"Liberty, equality, fraternity: it is vital to defend these values which are particularly threatened by the National Front," Julliard said, referring to Le Pen's party.
Julliard said Greenpeace was concerned about the "resurgence of nationalism" around the world, citing Turkey and Hungary as examples of countries where the right to protest had been curtailed.
Defending basic rights "is critical to continuing our environmental struggle" he added.
Friday's incident wasn't the first time that Greenpeace had carried out a stunt at the Eiffel Tower. In 2013 one of its activists spent hours suspended from the tower to protest against the imprisonment of 30 Russian militants after an operation on an oil platform.
The Eiffel Tower received around seven million visitors in 2015.
That figure dropped to six million last year as some tourists stayed away following terror attacks in France which have left 239 people dead since early 2015.